.308 chamber in a M305

lowgman

lowgman

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I've been contemplating a build for my M305 that's been collecting dust... I remember when I first bought the rilfe, I did some research and came to the conclusion that the 7.62 chamber in the M305 is not ideal to shoot commercial (or hand loaded .308) in.

Anyways - my quest is to build a match / .308 chamber in the M305.

How can I do this? Do I need to buy a USGI or a TRW bolt?

Can I lap the existing bolt to .308 headspacing? What are some of the negatives to this if it is possible?
 
1. Anyways - my quest is to build a match / .308 chamber in the M305.

Sure, you can make that happen if you have the $$.

2. How can I do this? Do I need to buy a USGI or a TRW bolt?

A TRW is a USGI Bolt...so is an H&R, Wichester, and some SA (Springfield Armory) bolts. You could also buy an aftermarket barrel (Krieger etc.) with a short chamber and have it reamed to .308 specs and use you M305 bolt.

3. Can I lap the existing bolt to .308 headspacing? What are some of the negatives to this if it is possible?

Lapping your existing bolt will only increase the headspacing. GI bolts are sometimes lapped if they are TOO TIGHT.

Most M305 rifles, even with "excessive" headspacing will fire commercial .308 for years with no problems. If possible, get your headspacing checked before you try any of the above...if it's close to mil spec I wouldn't worry about it...blaze away. YMMV...

Hope this helps...
 
I'm just looking for a tighter chamber so I can get more reloads out of the .308 brass. My understanding is that the 7.62 chamber stretches out the brass more than a .308 chamber.

If the avg headspace for a .308 is 1.630" - Is that what I should aim for?

Who sells the Keriger barrels?
 
BongoBob said:
1. Anyways - my quest is to build a match / .308 chamber in the M305.

Sure, you can make that happen if you have the $$.

2. How can I do this? Do I need to buy a USGI or a TRW bolt?

A TRW is a USGI Bolt...so is an H&R, Wichester, and some SA (Springfield Armory) bolts. You could also buy an aftermarket barrel (Krieger etc.) with a short chamber and have it reamed to .308 specs and use you M305 bolt.

3. Can I lap the existing bolt to .308 headspacing? What are some of the negatives to this if it is possible?

Lapping your existing bolt will only increase the headspacing. GI bolts are sometimes lapped if they are TOO TIGHT.

Most M305 rifles, even with "excessive" headspacing will fire commercial .308 for years with no problems. If possible, get your headspacing checked before you try any of the above...if it's close to mil spec I wouldn't worry about it...blaze away. YMMV...

Hope this helps...
Click to expand...

Yes - this does, thanks... I just have to get my head wrapped around all this headspacing...
 
lowgman said:
I'm just looking for a tighter chamber so I can get more reloads out of the .308 brass. My understanding is that the 7.62 chamber stretches out the brass more than a .308 chamber.

If the avg headspace for a .308 is 1.630" - Is that what I should aim for?

Who sells the Keriger barrels?
Click to expand...

Yes, a long chamber will stretch the brass a bit. You could also set up your dies to fit the brass to you chamber. An RCBS precision mic would help with this...it measures you fired brass, then you adjust your dies to move the case shoulder back enough to match you chamber...however, it is usually recommended that you "full length" resize your brass for firing in this type of rifle for function and safety reasons. A 1.630 would be a bang on match chamber.
I'm not sure who sells Krieger barrels.
 
From everything I've seen,the Norincos have excess headspace in relation to both .308Win and 7.62 specs.

Conventional wisdom has it that excessive headspace is not a good thing in any rifle. Just because the Norinco fans run this up the pole as "the new normal" does not mean that it is a desirable or acceptable condition. I sure would'nt accept it in any other rifle. If you wish to reduce headspace on an M14 type,there are only two alternatives. First, you can look for a longer bolt(not a likely fix in view of the excessive headspace which exists). Second,you can install a new barrel and then cut a minimum chamber(1.632 is generally recommended for a .308 gas gun) with a finishing reamer.

I don't see much dialogue on case separations in the Norincos,so people are obviously managing as things are. Shooting heavier MILSPEC brass is an added precaution. I like to handload for both accuracy and economy,so I prefer a tighter chamber in the interests of longer case life.

The reports on the new issue of Polytech rifles indicate that headspace is considerably tighter in these than in the Norincos.This is encouraging to the point where I'm tempted to finally take the plunge.
 
purple said:
From everything I've seen,the Norincos have excess headspace in relation to both .308Win and 7.62 specs.

Conventional wisdom has it that excessive headspace is not a good thing in any rifle. Just because the Norinco fans run this up the pole as "the new normal" does not mean that it is a desirable or acceptable condition. I sure would'nt accept it in any other rifle. If you wish to reduce headspace on an M14 type,there are only two alternatives. First, you can look for a longer bolt(not a likely fix in view of the excessive headspace which exists). Second,you can install a new barrel and then cut a minimum chamber(1.632 is generally recommended for a .308 gas gun) with a finishing reamer.

I don't see much dialogue on case separations in the Norincos,so people are obviously managing as things are. Shooting heavier MILSPEC brass is an added precaution. I like to handload for both accuracy and economy,so I prefer a tighter chamber in the interests of longer case life.

The reports on the new issue of Polytech rifles indicate that headspace is considerably tighter in these than in the Norincos.This is encouraging to the point where I'm tempted to finally take the plunge.
Click to expand...

I don't think anyone is saying excessive headspace is a good thing...it's just a reality of some of these Norinco M14 rifles, (and quite a few GI issue rifles as well) and many people have had absolutely no problems with them.
Keep in mind, these types of rifles are designed to function in "battlefield conditions"...lots of dirt, mud and crud and hopefully keep firing. A "match" chamber probably won't function as well in those conditions...but when will you ever really need it to?
A "longer" USGI bolt will pretty much always fix this problem. So will a barrel with a short chamber as suggested earlier. If you want a rifle with none of these problems, buy a bolt gun.
 
Before spending $600 to solve a non-problem, try setting your sizing die so it does not size the brass 100%. This means the shoulder is not pushed all the way back, after it has been fire-formed to be a perfect fit in your (long) chamber.

Then see if ammo made that way still chambers properly. if it does, you have ammo that matches your chamber, and should last long enough for you to lose it in the grass.

My M305 has +10 thou of headspace. I use a RCBS +6 though shell holder when sizing the brass, so the effective headpace of the loaded ammo is +4, a nice fit. have yet to have a case failure.

There are two kinds of 'excess" headspace. One is becasue the chamber is too deep. not a danger and easy to solve by not sizing brass back all the way.

The other cause is the bolt too short at the bolt face. This is dangerous, becasue the brass can let go.

BTW, if the bolt is too short but the chamber is cut a bit shallow, the headspace will read perfect, but the gun is still dangerous.
 
I don't accept that you need to have a bolt gun to avoid an excessive headspace condition. I've owned and/or built more than 30 Garands-and every one was set up with headspace within the .30-06 "no-go" limit. My HRA M14 has headspace less than 1.638 as do 2 Tipo 2 Garands which I've built in 7.62mm. For a 7.62 chamber I use a 1.634 308 Win "no-go"gauge as a "go" gauge and a 1.638 .308 Win "field" gauge as a "no-go" gauge.

This strikes me as a pi**-poor quality control issue and nothing more. Building a rifle with correct headspace is'nt exactly rocket science. A few less turns of the finishing reamer and some diligence with the headspace gauges is all that's required. If the freakin things are stamped and sold as .308 Win then the "go" chamber dimension is 1.630 and "no-go" is 1.634. Anything else is a balls-up.
 
purple said:
I don't accept that you need to have a bolt gun to avoid an excessive headspace condition. I've owned and/or built more than 30 Garands-and every one was set up with headspace within the .30-06 "no-go" limit. My HRA M14 has headspace less than 1.638 as do 2 Tipo 2 Garands which I've built in 7.62mm. For a 7.62 chamber I use a 1.634 308 Win "no-go"gauge as a "go" gauge and a 1.638 .308 Win "field" gauge as a "no-go" gauge.

This strikes me as a pi**-poor quality control issue and nothing more. Building a rifle with correct headspace is'nt exactly rocket science. A few less turns of the finishing reamer and some diligence with the headspace gauges is all that's required. If the freakin things are stamped and sold as .308 Win then the "go" chamber dimension is 1.630 and "no-go" is 1.634. Anything else is a balls-up.
Click to expand...

Yes, but you and I aren't working at the Norinco factory, are we? My GI TRW and HRA M14s both headspace better than your HRA...so what? My Norc with a HRA GI bolt and barrel spaces 1.632...so what?...good for me. No you don't need a bolt gun to avoid a headspace issue...just don't buy a Norinco M14 if you need to be fussy about that sort of thing...and #####ing about Norc quality control doesn't solve the problem.

I think you know exactly what I'm getting at by my prevoius posts...these guns will work as they are...If you want to tweak them to "match" specs, go for it...not that difficult to do. I also have a Norinco that I've done nothing to...works just fine thanks. If you want to avoid these issues, don't buy a Norc...to me, they're a good source of forged receivers for cheap.

This argument is as old as the hills on CGN. We all know that Norc quality control is not great, but for the money...who cares? If that bugs you, don't buy one! We can't take our GI M14's out shooting anymore, so now I'm getting my M14 kicks with a Norinco...better than not shooting one at all...yes?
 
Krieger barrels are brought in by obtunded our local CGN Krieger barrel importer! He is great to deal with.

I've just installed a Krieger Hvy NM barrel on a Norc receiver last week and it just closes on the 1.630" GO gauge. Life is good! Lots of good information posted above! ;)

:cheers:

Barney
 
I hear ya on wanting a 1.630 - 1.632 chamber, so i took Laz 2000's advice he gave me in a earlier post "go buy a GI bolt and have it fitted".;) I also obtained a GI oprod and barrel while i was at it.

I should add that i have always loved GI parts on my rifles and that is why im willing to pay the price (within reason anyways).
 
i took other people's advice and went on shooting with my extremely large chamber



disclaimer: i have alot of fun, maybe you won't experience the very same feeling.
 
Bongobob: I used the Norc bolt and fitted it with my finish pull through reamer. Now this Krieger will have a tight chamber and will shoot 'darts'.... :D
 
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