M48 Question - head spacing

[cruzans]

First, I apologize for my ignorance.
So, I picked up a nice M48 w/o bolt. Then, I found a nice complete bolt. From what I read, it isn't just a slap the bolt in and ready to go. Technically you have to check head space, etc, etc.. So, in regards to safety - is it "ok" to hit the range, slide the bolt in, check it to be sure it is secure, locks up nice, etc., and then give it a shot to see if it works? Or do you really have to let a gunsmith check it. Again, I know the standard answer that a gunsmith should check any firearm out if old and you are unsure - but if gun and bolt are in great shape and all seems to fit tight .......................

[762xIan]

While it "should" be safe, there is a slight chance something could be wrong. You could find a smith to ensure that the headspace is correct with a headspace gauge. It should not close on a no-go...but if it does, it absolutely should NOT close on a "field" gauge.

Personally I have "built" or parted together rifles before. With the first shot, I ensured the round chambered ok, upon firing I inspected the brass very closely. It is pretty easy to tell from the brass if headspace is excessive. Since I reload, you can measure the brass before and after and see how much the brass grows. I had a Enfield .303 that had excessive headspace and would have case seperations. But with measuring the brass and bolt head I was able to troubleshoot on my own and order a different bolt head to correct the headspace.

Once I really got into doing more smithing, I started acquiring some headspace gauges and have checked all my stuff out since then. If you really want to be safe I would call around to some shops and ask what they would charge to do a headspace check, it should be relatively cheap.

It is really up to you...be careful out there.

[R L Suehr]

If it were me I would either get a guage and check it or take it to a Smith first and have them check it out. As was said above, it shouldn't cost very much and will give you piece of mind. With the amount of stuff you pick up you might just want to buy some go no-go guages so you can check stuff out yourself. They aren't cheap, but aren't really expensive either.

[aubie515]

Always check headspace when you swap out bolts/bolt face. Older surplus firearms did not have the tight specs that today's firearms do. Why risk injury or worse when you can have piece of mind with purchasing gauges or paying a smith to check the headspace.

Firearms are dangerous and when you don't check things out before you fire an older firearm...it's just asking for trouble.

[lancelinked]

First, I apologize for my ignorance.
So, I picked up a nice M48 w/o bolt. Then, I found a nice complete bolt. From what I read, it isn't just a slap the bolt in and ready to go. Technically you have to check head space, etc, etc.. So, in regards to safety - is it "ok" to hit the range, slide the bolt in, check it to be sure it is secure, locks up nice, etc., and then give it a shot to see if it works? Or do you really have to let a gunsmith check it. Again, I know the standard answer that a gunsmith should check any firearm out if old and you are unsure - but if gun and bolt are in great shape and all seems to fit tight .......................

Your headspace should definitely be checked. The 48 design has decent gas venting, but there is nothing like a face full of 50KSI, a blown mag well, and a split stock to ruin your day.

Julian Hatcher tested increasing headspace for failure in 1949, and determined in the case of WW2 30-06 ammo in a 1919 (has adjustable headspace) that his batch of brass was able to retain gas by stretching reliably up to about 16 thousandths of an inch. Above that case head separation became increasingly more likely, until it was uniform at about 24 thousandths. That experiment indicates that we are pretty safe just closing on a "field" gauge (+6 thou) as acceptance criteria, even though most gunsmiths would reject such a rifle. A "go" gauge is as big as the factory spec for the cartridge, and means that your chamber is big enuf. A "no-go" gauge is generally 4 thou oversized, and is a reject test for factory guns. This standard is for bolt guns. Some autoloaders and machine guns run only with more open headspace.

The quick and dirty do it yourself test is done with scotch tape, a razor knife, and a dial caliper. Scotch tape is generally 2 thousandths of an inch thick, so two layers trimmed on the base of a factory cartridge would be a "no-go", and 3 layers would be a "field". The untapped cartridge is a decent "go". remember to remove the firing pin from the bolt (needs a through cleaning anyway) when doing such test with live ammo. If you can get 4 layers of tape you are at 8 thou (as the calipers will validate), so you need a different bolt.

Another important test on the 48 and on Spanish mausers, in particular, is the bolt set-back test. If you keep adding tape till it requires slight force to rotate the handle, then detect an increased force required to un-rotate it, this means that you probably have set-back in the receiver lugs. There is a more sophisticated test using a machinist's depth gauge with extension that should be done before such a receiver is scrapped, but we won't cover that here. I have seen M48 that had bolt set-back in the receiver lugs.

[edritchey]

If you want to bring it over I'll check it while you wait for nothing. Better safe than sorry if you want bring some ammo too I have a range here if it headspaces good you can try it out and see how she shoots. PM me if interested.

[Stooperzero]

could use the sized case/stick method.

[Stooperzero]

What was really interesting was the batch of Turk mausers that came in around 2002-2004 . The cosmo weighed as much as the rifle , They were cheap so you bought 2-3 at a time and you basically played match maker with the bolts until you got one that was safe .

[cruzans]

Thanks for all the info. tips ! Should have the bolt by Saturday!