Distance to lands and grooves

[lawdog]

I have a 6X45 18 inch standard length mid with a target crown. Hogue free float hand guard and low profile gas block. The rest of the upper is standard DPMS. Lower is Stag with A2 stock with Mil Spec Buffer.

I've been reading on here about mag length loads and just beyond. However, I haven't read anything about hard numbers or specs on where the lands/grooves will be on average from the bullet that is loaded to 2.260. I'm no beginner when it relates to handloading. I've loaded .300 RUM, .300 Win Mag, 7mm Mag, 35 Remington, 45-70 Gov't, 25-06, .243, 9mm, 45 ACP, .38 Special, and 6.5-06 Ackley Improved for a Thompson Encore. The latter was the most challenging because you have to fire form each piece of brass and set the head space exact or you will split the cases. All that aside, as you may have noticed, none of these were for a semi auto rifle.  

In my bolt guns, I would place a bullet of choice that had been blackened with smoke or a sharpie into a once fired piece of brass and seat it. Then I would slowly close the bolt until I felt the bullet hit the lands, and seat a little further in. Repeat until I had it exact. Then load at ten thousands off and start working up loads. 

That brings me to my main question. 
Is there a simple way to use an empty case and bullet to find exactly how far the lands/grooves are for one of these style rifles? It just seems that you can't use my method because of the bolt having to slam forward and lock into place...

[GLSHOOTER]

Our method of choice for finding numbers is the Sinclair Depth Seating Tool. The method you describe WILL work on an AR. You just don't slam the BCG home. You insert the round and lower the BCG with the upper off the gun then just push the bolt home with your finger pressure. Worked well for me until I found out the Hornady rig that requires the custom case, which I made up out of a 223 and reamed the inside neck before I got my own drill and tap to make them, to get a number. It was a bit of work but does better than the old method. Once I learned of the SINCLAIR set up the Hornady started gathering dust.

There has been a chamber redesign for improvement taking out some free bore last year. I would recommend you check it. MY old chamber was longer than the new one that I just received
Greg

[lawdog]

I ordered my barrel in Nov of 2012 and it took a while to get it to me. Then it took me a while to get everything together to build out the gun. So I'm sure that I probably have the longer throat. What did yours measure on average for the barrel that has the longer throat?

[GLSHOOTER]

I'll put some numbers up tomorrow but NOTHING hits the lands from a 2.60 magazine. Not even close.

Greg


On my early 2012 6X45 barrel

Distance to lands

58 VMAX 2.390
65 VMAX 2.384
HORN 87 2.375
SIERRA 90 2.474
BERGER VLD HUNT 95 2.558
BERGER 105 BT 2.471

[chesapeake]

I recently recieved a 20" 6x45 BHW barrel and started work ups. After reading all the past threads of stainless AICS mags, and loading out at 2.29+ AOL I was a little surprised when my sharpie'd up dummies were getting throat marks at 2.268 AOL with 85 HPBT's.
My method was to build a dummy, sharpie the ojive, then drop the round in and push the bolt home by thumb pressure. Charging from magazine with charging handle produces similar results.
With my Hornady gauges it looks like the Sierra 85 tip to ojive ~ .354, Nos 85 pt ~ .42, and Horn 87 bthp ~ .42.
With the 3 bullets I've played with 2.27 to 2.28 will be kissing lands (more like 3 lobes). The Sierra 85 will have .09 less jump at any given AOL compared to the other 2.

My barrel seems to be throated for standard 2.25 - 2.26 AOL loads.

I'm wondering if some of the Pro team could share the current chamber dimensions, or at least the throat/lead dimensions.

[GLSHOOTER]

Ogive shape has a lot to do with it. I don't have that bullet to meaeure but I'm sure it's not long and pointy like some listed above. As an example in the American 30 a 150 would hit at 2.295 but a 110 would hit at 2.008. This is one reason we highly recommend the use of tooling to get an idea before pulling the trigger.

I do know they were discussing pulling some of the free bore out so reaching the lands from magazine lenght was possible. It would appear from your anecdotal measurements they have done that. I have a 6X45 Savage barrel that should be done in the very near future so I can compare old vs. new. In this case you have a chamber that is a bit superior over the long one. I hope my bolt barrel is the same.

Greg

[chesapeake]

Yeah, I understand the ojive shape deal. Why I'm interested in the reamer geometry. Gives a solid point of reference.
Being able to reach the lands in magazine length loads is good.

A bit off topic but..
With my setup I'm crunching Benchmark and 8208xbr at anything over 25 grains in 2.260, LC brass, Sierra 85. Luckily my local temps don't seem to cause issue with H335, and I can fit plenty of it in the case.
Accuracy has been great. Just need a sunny day to chrono and see what velocity is doing.

[GLSHOOTER]

Feb 27, 2016 12:35:01 GMT -8 chesapeake said:

Yeah, I understand the ojive shape deal. Why I'm interested in the reamer geometry. Gives a solid point of reference.
Being able to reach the lands in magazine length loads is good.

A bit off topic but..
With my setup I'm crunching Benchmark and 8208xbr at anything over 25 grains in 2.260, LC brass, Sierra 85. Luckily my local temps don't seem to cause issue with H335, and I can fit plenty of it in the case.
Accuracy has been great. Just need a sunny day to chrono and see what velocity is doing.

You won't have any issues with BM or 8208 with the heat if my Arizona heat swings are any indication. I have shot 6X45 both loaded SHORT and LONG in the heat and saw nothing to be concerned about. YMMV

Greg

[geepee3]

Chesapeake,
I have two BHW 6x45mm barrels.
The first one I ordered was in December of 2013 and received in April of 2014 was an 18" mid-length standard contour.
Then I ordered a 20" rifle-length standard contour in September of 2014. Which was received in October 2014.
The 18" barreled AR is the one I shoot the most and have been testing with. 
With the SGK 6mm 85 gr. HPBT bullets. They engage the lands at 2.353".
Since the 20" AR has been more of a safe queen, to my shame , I pulled out the rifle to gauge it.
The SGK 6mm 85 gr. HPBT on the 20" barrel engage the lands at 2.272". No way to load at 2.295" in this one.
So I will most definitely have to qualify my measurements in the future.

Thanks,
Glenn

[GLSHOOTER]

And that's why I always use the Sinclair tool on every barrel I get regardless of the make.

Greg

[chesapeake]

Geepee3,
Your later barrel mic's out very similar to mine.