understanding head space (.22lr)

[Bradley J.]

On my recent project of a .22LR pistol I have hit a dead end. Everything is done except for the plating and the barrel. I should receive the barrel blank tomorrow or the next and I am fully aware of how to set it up correctly in my lathe the turn and thread it but after that I will need to chamber the barrel which is where my problem starts. I'm going to need to buy the chamber reamer and I don't plan on starting the barrel without all the proper tools on hand (why set up the barrel in the machine twice) I have checked out Brownells and a few other online vendors and I'm coming up with a few types of reamers. Some are "Match" and others say "Bentz" but all are .22LR reamers. What should I be looking for to chamber a barrel on a .22LR semi auto pistol? I'm not looking to make this gun a super accurate target pistol, I'm just making a hobby outa this and hoping to learn some new things (but get it done right)

Next on my question list is the headspace. I know the specs of a .22 round....

Case type Rimmed, Straight
Bullet diameter .223 in (5.7 mm)
Neck diameter .225 in (5.7 mm)
Base diameter .225 in (5.7 mm)
Rim diameter .275 in (7.0 mm)
Rim thickness .040 in (1.0 mm)
Case length .590 in (15.0 mm)
Overall length .985 in (25.0 mm)
Rifling twist 1-16

The rim thickness is .040 wouldn't I want .040 to stick out behind the barrel. Also I can't find any specs stating how much headspace a .22lr requires so I assume that the headspace will be different for each gun. I have found headspace gauges but they say for bolt action rifles (wouldn't it be the same?)

Any info would be appreciated thanks. I'm sure I'll have more questions once I think about this a little more.

 

[bpm990d]

You need to order The Complete Illustrated Guide to Precision Rifle Barrel Fitting by John Hinnant. It has a whole section on .22 reamers and specs.

The Bentz "Match" chamber is specifically designed to function in the semi automatic handgun or rifle.

His drawing of the Bentz chamber shows headspace as .043.

B

 

[Bradley J.]

Thanks. I was just browsing barnes and noble online. I need to take a ride tomorrow.

 

[bpm990d]

I don't think you will have much luck at any brick and mortar store. Just order it direct from Precision Shooting Magazine.

B

 

[Bradley J.]

The only other thing I can think of doing is getthe reamer and ream the chamber until it just comes in contact with the rear of the barrel. This is hard to explain but the stock barrel is made of the barrel and on the chamber end there is a counterbored block the barrel slides and press fits into. The block actually shows where the last chamber reamer stopped and since I'm only replacing the barrel not the block I could use that as a reference point on where to stop. It's a possibility but I did order a long barrel blank so I have plenty to practice on. I'll just wait till I get everything in.

What I don't get with the headspace gauges is they say with the go gauge the bolt will close but the no go the bolt won't close. This is a semi auto pistol not a rifle so there's no bolt to open or close.

 

[bpm990d]

Practical Machinist forum has a gunsmithing section. I'd post your question over there.

B

 

[oneswithfunes]

Get in touch with the nice people at Ptg They will set you up with what you need. If they don't have it they will make it. They make very good reamers.

 

[Bradley J.]

Problem solved. I took measurments of the stock barrel and now I know where it was. I'd like to know how to figure it out the right way but until then this will work.