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Gunsmithing Chambering for 308 v. 7.62

grunt0311

grunt0311

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May 25, 2008
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I have a TBA M40a3 that I shoot a lot and I love to shoot it. The issue that I am having is that I use Lake City brass in it. When I chamber a round it goes it tight. I have a life time supply of this stuff and want to continue using it.

When I do chamber a round that is Remington brass it doesnt chamber hard at all. Now I do know that the LC brass is thicker than commercial brass. Would this be the cause of the LC brass chambering hard? Would it be better to have the chamber recut for 7.62 since I am using LC brass? When I was in the sniper platoon I dont remember any rounds that we were using ever chamber this hard. I have about 1k rounds down the tube right now.

Any help or thoughts is appreciated. I am also getting ready to build my M40a1 and want to know if I should have it cut in 7.62.

Thanks
 
Re: Chambering for 308 v. 7.62

Your 7.62mm ammo should be headspaced to .308 spec., so it should fit nicely into a .308 chamber.

LC brass is thicker, but only at the web, so that shouldn't matter.

Is your LC brass once-fired in another rifle and not resized?
[The .308 Win Go Gauge is 1.630. The 7.62 is 1.635. The .308 No-Go dimension is 1.634. The 7.62 is 1.6405].

Have a read: http://www.303british.com/id36.html
 
Re: Chambering for 308 v. 7.62

if you look at the saami specs the differences between .308 and 7.62 are so mimimal you would never notice the difference with the exception of the free-bore which is longer on the 7.62 mm
 
Re: Chambering for 308 v. 7.62

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: coues103</div><div class="ubbcode-body">if you look at the saami specs the differences between .308 and 7.62 are so mimimal you would never notice the difference with the exception of the free-bore which is longer on the 7.62 mm </div></div>Not exactly. Chamber length could be a problem, but I don't think it is in this case as he is not using a semi-auto.
 
Re: Chambering for 308 v. 7.62

You could just run all your brass through a FLS die. If its still tight after sizing you might consider chambering. When building or rechambering, you first decide what bullet you want to shoot and then tell Dave Kiff at PTG to make a reamer for that round. You will get the best possible chamber that way.
 
Re: Chambering for 308 v. 7.62

I wouldn't chamber a rifle for a problem lot of brass.

LC 175's are not a trick load. A standard Palma Match chamber, or almost any .308 chamber for that matter, should shoot it quite well.
 
Re: Chambering for 308 v. 7.62

I have shot all the LC in the same rifle and have had this brass for a couple years now. I also do FLS and do the same for all the every brass that I reload wheather it be Remington or LC. I follow the Sierra manual when I do reload. I also both brasses the same. I use the 175 gr and load them as closely I can to the M118LR.
 
Re: Chambering for 308 v. 7.62

Are you measuring the shoulder set-back or just assuming that the FL die is setting back the shoulder? If the die isn't touching the shoulder the problem usually surfaces at between the second and fourth reload.
 
Re: Chambering for 308 v. 7.62

No I am not measuring the shoulder set back. Ill have to check that next time I reload.
 
Re: Chambering for 308 v. 7.62

You are complaining because .mil brass fired in someone else's .mil chamber, not sized to fit your chamber, won't close in your rifle?
 
Re: Chambering for 308 v. 7.62

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: _9H</div><div class="ubbcode-body">You are complaining because .mil brass fired in someone else's .mil chamber, not sized to fit your chamber, won't close in your rifle?

</div></div>

I dont understand what you are trying to say but I wasnt complaining. Just asking a simple question.
 
Re: Chambering for 308 v. 7.62

The simple answer to your simple question was given already, however that alone does not solve your perceived problem.

Give us more details and we'll see if we can help.
 
Re: Chambering for 308 v. 7.62

I didnt see if you answered his question about the brass coming from another rifle or not, but if it did....

I have the strong belief that once brass is fired in a chamber, it never goes into any other chamber.
I dont care if you "size" it or not.

Winchester brass is too cheap for anyone to be using range brass.

If you are buying Lakecity or getting it new somewhere, and can not afford winchester, then I dunno. Find someone with a 308 reamer(not min. spec) and have them hand ream out .001" It might close just fine afterwards.
 
Re: Chambering for 308 v. 7.62

Yes the brass was fired out of another rifle before I got it. I can afford the Winchester/Remington brass but I got a bunch of LC brass from a buddy of mine since he doesnt reload.

I can shoot the LC brass. It does fire in my rifle but when I close the bolt with a round in the chamber it is hard to close even though it does close and I can fire the weapon.

Keith, so you are saying that I should get new Winchester/Remington brass and fire it out of the then that way when I reload I wont have that problem. Or the second option is to get a chamber reamer and ream it out .001"?

Now when I build my M40a1, should give my smith a dummy round so that he can make sure that the bolt will close easy?
 
Re: Chambering for 308 v. 7.62

I had the same problem with some M118LR brass once-fired from M-24's. Ran it thru my Redding small base body die and problem solved.
 
Re: Chambering for 308 v. 7.62

It makes NO sense to ream your chamber bigger to fit some free brass. That might be the most absurd thing I have ever heard.

If you can not make the brass function with your rifle by annealing and sizing, then sell it or throw it away.
 
Re: Chambering for 308 v. 7.62

Ive had the same problem, it was with a .338 lapua. A Full Length sizing die would not size far enough down on the base of the case. Bought a Redding Body die solved the problem. I use redding body dies on anything I will FL size. Just some info from my experience.

Kc
 
Re: Chambering for 308 v. 7.62

If you buy new brass and use it, you should not have any issues if the rifle is headspaced correctly.

If it were mine and I just had to use LC brass that was tight, I'd run my regular 308win finish reamer in and hand turn out .001", as long as it doesnt go over No-Go length of course. Might help, might not. But again, I would just stop using someone else's used brass.

And about using a dummy round to build a rifle around... I will never headspace a rifle with anything other than Go and Nogo gauges for legal reasons. Not only that, but why build a $3000 rifle around someone else's used brass?


Just use new 308win brass in your 308win dude.
 
Re: Chambering for 308 v. 7.62

I think Im just going to use the Winchester brass. Seems to be more of a headache then what it really is.

I know you would never use a dummy round to headspace. Id use the Go No/go gauges first.
 
Re: Chambering for 308 v. 7.62

That TBA rifle will not be done justice with LC brass. The weight variation runs from alot to a hell of a lot. Win is good, Lapua is great. If you get the dies set up correctly, you can load it 50 times. I have done so with a TBA M40 A1. Just set the shoulder back from 1.5-2 thou and neck down .2 at first and .3 after about 15 firings. Trim as indicated, but not as much as most think. Mikes reamer is perfect for Lapua brass. You can just slide a bullet into the fired neck.
 
Re: Chambering for 308 v. 7.62

I would do some measuring comparison between the loaded rounds of each manufacture.

Measurements I would be paying attention are loaded neck diameter, case length, and whether or not the bullet is engraving into the rifling.

These measurements could in turn give me insight as to whether I need to turn necks, trim to a shorter than standard neck length, or seat my bullets deeper.

The LC brass is good brass, but your chamber may require some tweaking of the brass to ensure full compatibility. Better to find the cause and solve any problems than to simply take a guess and sideline what may be otherwise perfectly good components.

While weight variations can be an issue, they may or may not relate directly to the more critical factor, case to case volume variations.

I simply overfill a case with the intended powder, and weigh that case's capacity as measured in that powder. Cases segregated by volume in this manner can be trusted as being similar for reloading purposes.

Greg
 
Re: Chambering for 308 v. 7.62

I'll take all of the old LC brass you're not going to use anymore...

I haven't been playing this game as long as a lot of you guys, but the idea of cutting a chamber some more to fit some brass is a NEW ONE on me.... WTF am I missing here?

From my experience, I can necksize only a few times, and then the bolt starts to get tight. Rather than properly sizing the brass when this occurs, I should be CUTTING MY CHAMBER DEEPER???????????

Seriously?? Am I high/drunk right now or something, or am I actually reading you correctly???
 
Re: Chambering for 308 v. 7.62

If the issue is the sizing die not setting the shoulder back it my show up after several firings with the Winchester brass also. Take a Lake City case and mark the shoulder/neck area with a majic marker, lube and size. You should be able to see if the issue is the die. I have used a bunch of Lake City brass in several calibers and in fact did have one die that would not touch the shoulder. Different die or a small ammount removed from the bottom of the die cured the issue. Old timers moment do not remember which. We have not even touched on the fact that all shell holders are not created equal. Bottom line when you modify anything it is wise to start with the cheapest part first.
pavementends
 
Re: Chambering for 308 v. 7.62

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: pavementends</div><div class="ubbcode-body">If the issue is the sizing die not setting the shoulder back it my show up after several firings with the Winchester brass also. Take a Lake City case and mark the shoulder/neck area with a majic marker, lube and size. You should be able to see if the issue is the die. I have used a bunch of Lake City brass in several calibers and in fact did have one die that would not touch the shoulder. Different die or a small ammount removed from the bottom of the die cured the issue. Old timers moment do not remember which. We have not even touched on the fact that all shell holders are not created equal. Bottom line when you modify anything it is wise to start with the cheapest part first.
pavementends </div></div>

Good answer. Honestly, a serious reloader needs to have an adjustable case gage! In this situation, it would quickly and accurately allow the reloader to determine how much, if any, the sizing die is moving the shoulder. If it is in fact moving the shoulder, the problem could be the following:

1. Brass too long, is being "forced" into the leade of the chamber - solution: trim brass
2. Bullets are seated too long, and are being forced into the rifling and/or being pushed into the case
3. Body of the case isn't being sized down enough - solution: small base die
4. And of course, the unlikely out-of-spec chamber

As much as I'd like the OP to give me all his "bad" LC brass, I coudn't do take it in good conscience. There is nothing seriously wrong with either the brass or the rifle, simply that he is not properly sizing the brass as required.

I still can't believe people are telling this guy to cut his chamber! As one person stated "Most absurd thing I've ever heard"....god!
 
Re: Chambering for 308 v. 7.62

The OP has not stated what the brass was originaly fired in. If it was a MG or very loose chambered rifle, it might not be resizable or require a small base die. I have seen no LC match brass that was worth the effort. I have no interest in comparing weight to capacity etc.
I can say if you want some average groups, you can get a great start on it by aquiring some below average LC brass. You can be average in no time.
 
Re: Chambering for 308 v. 7.62

Geez I am shooting Fed brass that I shot 3 other times in my old barrel/chamber in my new Lilja barrel. I just small based sized it turned the necks and worked up a load them loaded 600 rounds of it. I never had a single issue. It shoots little tiny groups.
 
Re: Chambering for 308 v. 7.62

I just got back from the field late last night and so today I am reading this and seeing some good ideas.

First off the brass that I am using has been shot out of bolt guns. The heastamp is marked as such LC MATCH 96, LC MATCH 95, LC LR 03, and LC LR 05.

I do have a some questions though. What is a small base die?

Turbo54 to answer some of your questions here they go.
1. I do check all my brass before I reload it to make sure that its not too long. I use the Sierra reloading book as a reference and I trim my brass to 2.010.

2. I check the bullets to start off with to make sure they are not too long but I keep them at 2.785 is where they are at now.

3. Ok your solution was small base die. Not sure what it is so thats a question I asked.

4. The unlikely event that the chamber is out of spec. God I hope not. I have used a Go/No-Go gauge on it and it is fine on both of those.

Pavementends next time I do reload Ill make the shoulder of the case and see if in fact it is touching the shoulder of not.

I do also have 5.56 LC brass as well that I have used for many years now in my Colt AR15 and I havent had the problems with that like I do with the 7.62 brass.
 
Re: Chambering for 308 v. 7.62

USMC Grunt - thanks for your commitment of service to this exceptional country!

A small base die is a sizing die that sizes the body of the case several though under spec. Seems doubtful you need it but maybe. The best thing you could do for yourself is get a case gage. That said, your trim length of 2.010 sounds fine. OAL of 2.785 sounds fine. Sure does seem like youre either not buping the shoulder enough or not sizing your body enough...

Are you setting your die/press to "cam over"?
 
Re: Chambering for 308 v. 7.62

Turbo54 I do appreciate the support from you guys. I am gtting ready to go on deployment #6 so should be another fun one.

For my reloading dies I am using the RCBS. It has 2 dies, 1 to deprime and size and the other to seat the bullet.

What is a case gage and do you have an item number or place I can get one?

Also please expain what you mean by "cam over"?
 
Re: Chambering for 308 v. 7.62

Does your sizing die say :

1. "FLS" or "Full Length" or
2. SB or Small base or
3. Neck

???

A case gage is a size checking tool. They come in two flavors, adjustable and nonadjustable. The nonadj type is basically a precision machined "chamber cut to minimum and maximum SAAMI specs for you to drop a sized case into. It is machined so that with a case instqlled, the casehead should be flush, or sub-flush to the end of the gage, or else your the case headspace is too long. If it wont drop into the gage easily, the body isnt sized enough.

The adjustable gage has a micrometer knob that will additionally tell you how MUCH your hwadspace is off.

By "camming over", I am referring to the phenomenon you get when typically setting up a sizing die: you install shellholder on the ram, you run the ram all the way up, you thread the die in until it contacts the shellholder, and then you run the ram down, then thread the die in a LITTLE more. Set up this way, when you run the lever, you feel it get very tight ALMOST at the end of the ram upstroke.....but....you can still pull the lever just a little more.

Setting your die this way gives MAXIMUM sizing. Sometimes more than you need. Sometimes not enough! To size less, you back the die off. To size more, you'll either need to buy a thinner shellholder, to grind a LITTLE material off the bottom of your die, or grind/sand a LITTLE material off the top of your shellholder.
 
Re: Chambering for 308 v. 7.62

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: USMC Grunt</div><div class="ubbcode-body">I am gtting ready to go on deployment #6 so should be another fun one. </div></div>


Damn man.
Thank you.
 
Re: Chambering for 308 v. 7.62

Just checked my dies and the one has FL and then a 9 after it. I dont know what the 9 means.

Do you have a place where I could get a case gauge. I want to look into one to get. Which one do you prefer?

Now the "cam over" I know what you are talking about. Thats how I started is how you explained it. Now I do remember a couple months ago that I had to back off of it a little bit and I think I did that because I had a hell of a time getting the case out of the die. Then I added more case lube and it made it easier but I do think that I need to go back and lower the die a little bit more. I think first that I will check it with a magic marker first just to see how far off it is.


Thanks for the advice.
 
Re: Chambering for 308 v. 7.62

Turbo and everyone else that helped me out with this.

I worked on some reloads today. First off I marked a couple cases with the magic marker and then used the sizing die. It didnt touch the shoulder at all. So then I lowered the die a LITTLE bit and tried it again and the marker was rubbed off a little bit. So then I loaded two rounds went outside and loaded then in the gun and put one in the chamber. WOW!!! Wouldnt you know it worked. So I cycled the first round out and put the second one in and it went in smooth. So now Im adjusting the die a little bit so that it doesnt do the shoulder too much.

With that being said can I size the shoulder TOO much? Im wondering after all the brass that I put in the chamber like that if I screwed up the chamber at all or even messed with the headspace. I say that because some of the brass went in pretty hard.

So I think Im going to play around with it one round at a time and see what works best. I also put this in my M40 as well and it didnt chamber hard at all. So I think that I have something going here.

To all the guys that helped I say thanks. If anyone else has some comments or suggestions please put them here. Thanks!
 
Re: Chambering for 308 v. 7.62

I am sure tou didnt damage your rifle. If you did, it would manifest itself as galling on the rear faces of the lugs on your bolt.

The downside to sizing too much is less brass life. In extreme cases, it can cause a case head separation (CHS), but it sounds like your die/shellholder/press setup isnt really going to allow for very much more than just adequate sizing.
 
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