Help me cut down and recrown a .17hmr heavy barrel.

[12 Volt Man]

Cutting down a barrel and re-crowning.

I shot a Marln .17hmr the other day that the guy had had the bull barrel cut down to 18 inches and re-crowned by a gunsmith. The guy was charged $75.00 to have this done. Reasons for doing this were as follows. 1) it looks very cool 2) supposed to increase muzzle velocity and not affect accuracy.
He definately had an accurate gun.

After shooting and seeing this gun, my Brother In Law and I decided we each had to have one. I'm going to get the CZ 452 Varmint, and he is going to get the Savage with the heavy barrel. We want to have the barrels shortened.

I am looking for tips and best practices to get this done. Maybe a link to a tutorial of sorts. We just got a Smithy Metal Lathe/Mill combo that we could use. I know very very little about recrowning etc.....

Go for it? Or pay the $75.00 bucks to the gunsmith?

 

[Jim Watson]

Well, if you cut it off yourself and mess up, you can probably pay the $75 to have a gunsmith fix your mistakes.

Brownells has books and videos on machine tool operation.

 

[macavada]

How does shortening the barrel increase muzzle velocity?

 

[litman252]

if your luck is like mine, I'd start at 20"
I'm dong the same on a Mauser.
Tony

 

[larryw]

Thinking is that on some cartridges, powder burn is complete long before bullet exits bore and friction will slow bullet down. I'm sure proof of and exceptions to this thinking abound.

 

[stans]

Larryw is correct. With fast burning powders you can get complete combustion and actually see the pressure begin to drop before the bullet exits a long barrel. At this point friction can slow the bullet. But if you use a slow burning powder, it may not be fully combusted by the time the bullet has left the barrel. It is case of matching the powder burning rate to the barrel length.

 

[macavada]

That makes sense. Does anybody have any data for the 17 hmr specifically? What is the optimum barrel length?

 

[macavada]

To follow up on my last question, I was browsing rimfirecentral. Someone over there stated that 20" is the optimum length for the 17 hmr to reach full velocity. I didn't see a source. The stat was incidental to the post, not the main point.

... just in case anyone was wondering.

 

[ice]

The guys at Bullberry have a chart posted where they cut a 17 HMR Bullberry barrel off one inch at a time and checked velocity after each cutting.
Maximum velocity was at 19 inches.

 

[macavada]

Thanks for posting, ice.

 

[Onmilo]

Once you get it cut down the barrel facing and crowning tools Brownells sells are excellent for finishing things up.
From what they advise, the 79 degree barrel crown is optimum for the .17 caliber guns.