Gunsmithing How sloppy are the factory Remington .308 chambers

[LoneWolfUSMC]

I got to thinking the other day....

When I reload I usually only neck size my fired brass. I have enough that none of it is past it's second firing yet so no problems there.

I noticed awhile back that in my 700 I could only load 4 rounds in the magazine and still have the top round feed reliably. If I loaded five the bolt would ride over the top round. (this was with the "tabs" on the follower ground off).

Now circumstances have changed and I have started shooting FGMM for department funded training and duty use. With FGMM I can load five and have the top round feed 100% of the time.

This got me to wondering. So I broke out the calipers last night. I found that about 5mm up from the head of the case the fired cases are .005" fatter than the new unfired FGMM. Now I didn't think that much of a variance would cause the failure, but that is about all I can lay it on since the dimensions are otherwise the same between the FGMM and my reloads.

When I install my Williams bottom metal I will most likely shim and bed it to account for the difference and allow my reloads to feed from the magazine.

Now my question is really two-fold. First, are the remington chambers excessively large in diameter? Second, how much clearance is necessary for 100% reliability in field conditions?

Just some things I am trying to wrap my head around while I plan for a future rebarrel.

It's amazing how much of the small stuff just doesn't matter when you are shooting an issued gun with issued ammo. I never sweated any of this stuff with my M40A1 and M852. I just knew I could load five and still close the bolt on an empty chamber. Never bothered to look at the brass after firing unless there was a failure.

 

[MontanaMarine]

Re: How sloppy are the factory Remington .308 chambers

My brass is about .006" fatter ahead of the web, and .007" fatter just behind the shoulder, than a virgin military round.

Mulitply that times 5 rounds, it's a difference of about .030-.035". A little less total I suppose since the rounds are staggered in the magazine.

 

[LoneWolfUSMC]

Re: How sloppy are the factory Remington .308 chambers

Is that from a factory or a match chamber?

 

[MontanaMarine]

Re: How sloppy are the factory Remington .308 chambers

Factory chamber. Rem 700 VS.

 

[skeetlee]

Re: How sloppy are the factory Remington .308 chambers

Any remington 700 rifle i have ever owned had big sloppy chambers... Go custom, it doesnt cost that much more.

 

[MontanaMarine]

Re: How sloppy are the factory Remington .308 chambers

I neck size too, so it's really not an issue. If anything i'm gaining a little more room for powder.

 

[sinarms]

Re: How sloppy are the factory Remington .308 chambers

if your chamber was oblong it would make it hard to chamber a neck sized only round.

 

[RoughNeck182]

Re: How sloppy are the factory Remington .308 chambers

Sorry if it's not entirely relevant but once fired brass from my Rem 700 in .243 measure ~0.007" larger just below the shoulder (0.458" once-fired vs. 0.451" unfired factory ammo). The cartridge dimensions listed in the Lyman 49th edition reloading book splits the difference almost perfectly. I found it interesting that right above the recessed part of the rim it is larger than unfired but is 0.001" SMALLER than the cartridge specs from the book.

 

[LoneWolfUSMC]

Re: How sloppy are the factory Remington .308 chambers

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sinarms</div><div class="ubbcode-body">if your chamber was oblong it would make it hard to chamber a neck sized only round. </div></div>

I would think you would have to really screw the pooch to accomplish that with a round reamer and the correct setup.

 

[BLAWTON]

Re: How sloppy are the factory Remington .308 cham

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: LoneWolfUSMC</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sinarms</div><div class="ubbcode-body">if your chamber was oblong it would make it hard to chamber a neck sized only round. </div></div>

I would think you would have to really screw the pooch to accomplish that with a round reamer and the correct setup.

</div></div>

Its just about inpossible to oblong one. The reamer would have to be moving all the time. Most likely the chamber would become oversized then become oblong. I have seen factory chambers that have been .02" long though....