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Post by blamm1009 on Oct 10, 2016 14:34:25 GMT -8
I have been digging around this site for a few months now while getting my 243lbc built. Final build is a BHW 243lbc 24" semi-bull barrel with an Aero upper and lower. I finally got to shoot it this weekend and I am having a few problems that I cannot find answers to using the search function. I started with an optimum charge weight test after about 20 break-in rounds through the barrel using TAC powder, CCI 400 primers, new Hornady brass, and Berger 95gr VLD hunting. Started at 27.7gr and stepped up in 0.3gr increments to 29.2gr. The rifle shot fantastic but a few things concern me. Sorry in advance for the long post. First, every primer is cratered from the lowest load to the highest load and none seem worse than the others. They are not flattened at all so it does not appear to be a pressure issue. I am using a 7.62x39 bolt carrier group. Pictures below. Is this a bolt issue, a primer issue, or a pressure issue? I use these primers in my 223 pushing a 77gr pretty hard and don't see this issue. The second issue is that I am only getting about 2775 fps on some of the hottest loads. I am worried about pushing it much farther with the primer issue stated above but I feel I am still way under the max on this cartridge. Again, no pressure signs such as flattened primers, just the consistent cratering. My research has been telling me that with a 24" barrel I should be expecting a little more speed out of this round. The next issue I am experiencing is gouging of the bullets when feeding from the magazine. Every round that I have pulled out of the chamber has a significant gouge on the bullet. feeding it through the magazine again adds yet another gouge to it. It appears to be coming from the barrel extension. Do I need to round off sharp points or something? Pictures below. Along the same line is another issue. I purchased the recommended ASC 10 round magazines but with the bolt locked to the rear and a magazine inserted it will not strip the first round off if I just drop the bolt. I must pull the charging handle back to its furthest point to get it to catch a round. Not a huge issue but I wanted to know if this was common. All in all the round is very stable across almost the entire charge range I chose, not shifting point of impact at all. Once I was done I had 4 rounds left from my barrel warmer/sight in bunch I pushed it out to 400 yards on steel and it was just one black smudge where all 4 rounds impacted right on top of each other. I can't wait to get the bugs worked out and put this gun through it paces at a PRS match. Thank you all in advance for any help!  |
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Post by Deleted on Oct 10, 2016 15:13:30 GMT -8
I have been digging around this site for a few months now while getting my 243lbc built. Final build is a BHW 243lbc 24" semi-bull barrel with an Aero upper and lower. I finally got to shoot it this weekend and I am having a few problems that I cannot find answers to using the search function. I started with an optimum charge weight test after about 20 break-in rounds through the barrel using TAC powder, CCI 400 primers, new Hornady brass, and Berger 95gr VLD hunting. Started at 27.7gr and stepped up in 0.3gr increments to 29.2gr. The rifle shot fantastic but a few things concern me. Sorry in advance for the long post. First, every primer is cratered from the lowest load to the highest load and none seem worse than the others. They are not flattened at all so it does not appear to be a pressure issue. I am using a 7.62x39 bolt carrier group. Pictures below. Is this a bolt issue, a primer issue, or a pressure issue? I use these primers in my 223 pushing a 77gr pretty hard and don't see this issue. The second issue is that I am only getting about 2775 fps on some of the hottest loads. I am worried about pushing it much farther with the primer issue stated above but I feel I am still way under the max on this cartridge. Again, no pressure signs such as flattened primers, just the consistent cratering. My research has been telling me that with a 24" barrel I should be expecting a little more speed out of this round. The next issue I am experiencing is gouging of the bullets when feeding from the magazine. Every round that I have pulled out of the chamber has a significant gouge on the bullet. feeding it through the magazine again adds yet another gouge to it. It appears to be coming from the barrel extension. Do I need to round off sharp points or something? Pictures below. Along the same line is another issue. I purchased the recommended ASC 10 round magazines but with the bolt locked to the rear and a magazine inserted it will not strip the first round off if I just drop the bolt. I must pull the charging handle back to its furthest point to get it to catch a round. Not a huge issue but I wanted to know if this was common. All in all the round is very stable across almost the entire charge range I chose, not shifting point of impact at all. Once I was done I had 4 rounds left from my barrel warmer/sight in bunch I pushed it out to 400 yards on steel and it was just one black smudge where all 4 rounds impacted right on top of each other. I can't wait to get the bugs worked out and put this gun through it paces at a PRS match. Thank you all in advance for any help! Lets take these in order. Your first problem is your not using the correct primers. CCI 400 are to thin for an AR. Your load isn't to hot, your primers are to soft. Try some CCI 450's or some Remington 7 1/2's. That will correct your primer problem. This will also let you work up to a load with more speed. If you are experiencing gouges on your bullets and brass, ( which is not uncommon ) break all the sharp edges with your Dremmel and a sanding drum. Follow up with a polish wheel and smooth it all out. Your magazine problem seems to be an ASC problem. I would give them a call. Explain the problem and I would bet they send you a new magazine. It's not uncommon for a 10 round ASC to only hold 9 rounds. Give these suggestions a try and get back to us. I would bet you'll be a happy camper |
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Post by GLSHOOTER on Oct 10, 2016 15:45:14 GMT -8
Change powders for better velocity and everything Ritch said is spot on. I'm running 2933 with 95 SMK's in my LBC shot single shot in 500 yard matches.
Greg
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Post by blamm1009 on Oct 10, 2016 16:21:28 GMT -8
Thank you guys for the quick response! I will make these changes and get back to you. I'm assuming that IMR 8208 is the powder you recommend changing to? Could you possibly PM me a min/max charge range for 95gr pills so I can have a starting point to work up to? I'm an avid reloader and am always cautious with load data but this is my first wildcat cartridge.
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Post by zr600 on Oct 10, 2016 16:35:05 GMT -8
I would just change one thing at a time. Get some cci 450 primers or Remington 7 1/2s. I used tac in my 6x6.8 with 87 g hornadys and they produced more velocity then 8208 did not by much but I broke 3000 fps with a 22" barrel with tac could t get above that with 8208. My final load with tac and 8208 ended up at 2950 for the best accuracy.
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Post by blamm1009 on Oct 10, 2016 17:49:31 GMT -8
I don't mind starting a load from scratch. I have been wanting to try 8208 for an alternate load anyways. I already use TAC for 223 so I figured I would see how it did while breaking in the barrel.
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Post by GLSHOOTER on Oct 10, 2016 18:05:13 GMT -8
I don't mind starting a load from scratch. I have been wanting to try 8208 for an alternate load anyways. I already use TAC for 223 so I figured I would see how it did while breaking in the barrel. I'll send some data tomorrow. Greg |
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Post by blamm1009 on Oct 26, 2016 7:08:55 GMT -8
Hunting season has drastically slowed down progress on getting this rifle up and running but I have a few updates and some problems that are still not resolved and need advice on. Please stick with me, I know this is a long post. First improvement, the barrel extension had some very sharp edges on it causing the bullet gouging. After a little grinding and a lot of polishing the issue has been resolved completely. Pictures below. Thanks for the advice on that one! Second improvement, switching primers to Remington 7 1/2 and powder to 8208 my velocities are much better and still no signs of pressure pushing 2975fps. However, even using the recommended Remington 7 1/2 primers I am still seeing cratering. I suspect this is a bolt issue of some sort but not a critical one since I am still not seeing flattened primers at all. Comparison pictures below as well. One of the biggest problems I am having, and have had since the start, is with cycling, brass getting stuck in the barrel/very hard to remove, and having to jam the bolt forward to get it to close all the way. I suspect this all is related to the bolt, which is a SMI 7.62x39 complete BCG (what my local shop had in stock), and here is why. Let me know if I am way off base. First caveat is that I am using Hornady brass because I had a bunch of brand new 6.5 Grendel given to me so that is what I am working with until I can afford to buy at least 300 pieces of Lapua. I am not seeing the overly thick neck that seems to have been an issue in the past with the Hornady. My neck diameter with a loaded round is fairly consistently 0.271" which I have seen is about right with the chamber being 0.273". The first issue is that when I go to load a round, the force of releasing the charging handle from the furthest back position is not enough to seat the bolt over the back of the round about half the time, even if the round is already in the chamber. I must use the forward assist to close the bolt. I know this is not a shoulder or neck issue because I have sized pieces of brass fired through the rifle to: set the shoulder back .010", trimmed the brass to a length of 1.450, and used the smallest bushing I have to size the neck down to .266" and the issue is still there. The second issue is that once a round is chambered it is very hard to extract it without firing, this is present even on the same modified pieces used above. I sometimes have to resort to slamming the butt of the rifle on the ground while using a lot of force on the charging handle. The issue is not present with and empty chamber so I suspect it is something to do with the extractor clearance and which I suspect is possibly the cause of issue described above too. Lastly, the reason rounds are not feeding out of the magazine is because the bolt is not cycling back far enough to catch on the bolt face but rather is catching on the face of the carrier. this is why pulling the charging handle back further is allowing rounds to feed. The gas block is opened all the way so I suspect this issue is due to the force required to extract the round from the chamber or the bolt being and overly tight fit with the round in it and getting stuck in the barrel extension. Does this sound like I am on the right track? If so which bolt is reccommended as a replacement? Thanks again for all your help! I really appreciate it! Attachments:
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Post by peabody on Oct 26, 2016 20:35:02 GMT -8
Have you measured the depth of the bolt face? It should be 0.125". If it's less, that will make for a tight fit of the round in the chamber. If, by chance, you have a 0.136" depth, that's the wrong bolt for the job. I had an issue with a 5.45x39 build involving the bolt face depth, as there was no standard among manufacturers when that round was transferred to the AR platform. My first bolt was too deep (0.136", if I recall correctly). After calling the barrel mfg regarding the issues I had experienced, I came to find that the bolt from another company was not compatible with the barrel due to the bolt face depth (it was designed for 0.125").
As for the bolt locking issue, I've had that type of problem occur with heavy magazine springs (too much upward pressure/friction on the bolt sliding over the rounds), a heavy buffer spring and/or a heavy buffer. But if you're rounds are hard to extract, that could factor into the bolt locking issue too...
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Post by blamm1009 on Oct 27, 2016 14:20:03 GMT -8
So I spent a little more time with this and tried a few things, including removing the extractor and closing the bolt on a piece of sized, once fired brass (through this chamber), bumping the shoulder back .010". The problem was still there so I watched carefully while tapping on the back of the BCG (upper removed from lower) and the problem was with the bolt trying to cam into the lugs. It was very tight and gritty as if there was not enough clearance/headspace since the problem does not exist with an empty chamber. I did measure the bolt face which is .126" deep from the face of the lugs. I don't have any indications on the barrel that it was a special type 2 headspacing (I purchased the barrel brand new from a local shooter who scrapped this project so I had to check) so I have to assume it is a type 1 headspacing. I inspected the backside of the bolt lugs and they were rough with machining marks so... I used a jewelers polishing bit (fine abrasive impregnated rubber) and polished the back of the lugs until smooth and testing operation after every passes. It took about 15 minutes of polishing, not including time between passes, but it finally closes on a piece of brass smoothly, with moderate force, and without the extractor installed. With it installed I still need to tap the bcg a little to get it to seat the brass into the bolt face but the force of dropping the bolt into the upright receiver is enough to overcome this most of the time so I should be better now. Round extraction is also much smoother and requires a lot less force. I'm not sure if this was the right thing to do but all reputable sources of 7.62x39 bolts are currently unavailable so this will have to do for now. I plan on purchasing a bolt from Young Manufacturing once they are in stock. Picture of the polishing attached. Attachments:
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Post by GLSHOOTER on Oct 27, 2016 14:49:13 GMT -8
I think you are on the right track. A range report will be interesting.
Greg
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Post by peabody on Oct 27, 2016 15:51:17 GMT -8
I'm not sure if this was the right thing to do but all reputable sources of 7.62x39 bolts are currently unavailable so this will have to do for now. I plan on purchasing a bolt from Young Manufacturing once they are in stock. Picture of the polishing attached. I'll recommend this bolt: www.blackriflearms.com/762x39-Melonite-QPQ-Bolt-Assembly-_p_239.htmlIt's in-stock and on sale right now. I bought my 2 piston uppers from this company and am only recommending them because I know they are very stringent on the quality of the parts they sell. I would buy it for my own rifles. I'll stop at that... |
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Post by GLSHOOTER on Oct 28, 2016 10:24:48 GMT -8
Out of curiosity do you have the rubber bumper in the extractor? Have you dehorned the extractor?
Greg
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Post by blamm1009 on Oct 31, 2016 13:48:52 GMT -8
Greg,
I have removed the rubber bumper from inside the extractor spring. It didn't really make much change on how hard it is to get the extractor to open and let the round seat but... since the other polishing I did, it isn't enough to stop the bolt from closing anymore. I'm not sure what you mean by "dehorning" the extractor, could you please explain? I did lightly polish the face of it where the round hits during chambering but only a polish. The problem seems to be that the extrator is too thin where it rests on the bolt face allowing it to hang inboard too far and this is causing extra force required to move it away far enough to seat the brass since it is hitting further up the ramped portion.
Range update,
I have done some additional Optimum Charge Weight (OCW) testing at some hotter loads (above the recommended range you gave me in PM) in an attempt to find the upper limit of this cartridge. Interestingly, I found another node with a velocity average of 3080 fps and still no signs of pressure! I have about 2gn of case capacity left but I think I am happy with that since it seems to still be easy on the brass. I also did some seating depth testing at the same time, round robin style like the OCW, and found that it does best around 0.040 to 0.060" off the lands. It was with a powder charge that gave me a good node at a lower velocity so I will be doing another test with a narrower range to find the depth my rifle likes best with the hotter load. I have found that these VLD's really like a good jump if you can't get them into the lands, which I can't with my barrel unfortunately. the closest I can get is 0.030" at max magazine length. My 6.5 Creedmoor bolt gun loves it 0.045" off the lands.
One awesome thing to note is that the worst group this rifle has shot through all of this is about 0.8 moa, with most hovering around 0.4 to 0.6 moa. It is making it hard to choose the optimum load when they all shoot really well and don't shift much at all. Just goes to show how resilient this load is to slight deviations allowing for seating depth variations and powder lot changes.
With the cycling issue sorted out I turned my attention to the cratering on the primers. After a few minutes with of playing with my calipers I found that the bolt is about 0.030 shorter than other AR15 bolts I have. This allows the firing pin to protrude 0.050 past the bolt face while other bolts only allow 0.020. This is the same with multiple firing pins as well. It seems that a common issue with rifles chambered in 7.62x39 is that they have too light of a primer strike for some steel cased or military ammo. I assume this is a purposeful design for better ignition since some people sand down the back of their bolt for this exact reason. I am fairly certain this is the reason for my primers cratering.
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Post by GLSHOOTER on Oct 31, 2016 14:09:50 GMT -8
Ritch has a thing about dehorning on the forum here I believe. Basically you are rounding off the outside horns on each side of the extractor. This often helps on feeding. These rounds don't like a whole lot of extractor pressure.
The long pin protrusion is common on the 7.62X39 bolts because of the hard primers. They are called enhancdd. I have those and bolts that are not enhanced. Try swapping out a standard 223 firing pin and see if that helps. The collar is usually located lower on the shaft than on the enhanced and you will get less protrusion. It's worth a trial.
Your accuracy is on par for what I would expect. My load levels are rarely MAX MAX. There are several reasons for that with brass life being very important.
Greg
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