AI Barrel De-Spigot

[Danpd]

I've chopped and threaded more than my fair share of AI barrels over the last 2 years, but this is the first time I've done this.

 

Customer wanted to keep the full 26" of his new .260 Rem barrel, and the M18 x 1.5 Standard muzzle thread, but didn't want to have the 23mm long AI spigot on the end of his barrel.

 

Initially I was asked If I would re-profile the blank to blend the spigot in to the rest of the barrel, this would have worked, but seemed overkill so I came up with this idea.

 

I Mic'ed up the existing spigot at 21.08mm, then turned and bored a sleeve from a piece of AI .338 barrel I had lying around from a 20" chop down. I made it 0.04mm smaller in diameter than the spigot. Quick burst of heat on the sleeve, some welding gloves and a trip to the hydraulic press, and we had a shrink fitted oversize sleeve on the existing barrel spigot.

 

 

Next the barrel was dialled in off the grooves to within .0002 as usual and crowned with the AI 11mm recessed crown. I also trimmed the excess material from the face of the sleeve and refaced the existing thread shoulder by approx .005 to clean it up.

 

 

 

 

 

As you can see from the pictures the sleeve was basically a seamless fit to the barrel. With only the slight variance in steel metallurgy giving it away (the .260 is a Lothar Walther, the .338 donor piece a Border)

 

Next step is to dial in the OD of the barrel as this is the feature we want to blend in to, and all operations requiring concentricity to the bore have been completed.

 

 

Then its time to remove some material from the sleeve OD in preparation for tapering. At this stage I also make sure my tool wear offset is Johnny on the spot by cutting to a non-critical oversize dimension and checking the actual dimension versus the programmed value. In this instance I made a correction of 0.037mm in the control to get the tool back on the money.

 

 

 

A couple of measurements and a little bit of trigonometry later tells me that the taper of this barrel is .464 degrees, combined with the measurement at the barrel shoulder, and I can calculate the required chamfer to blend the sleeve into the existing contour.

 

 

 

Heres a video of the lathe roughing and cutting the taper.

 

 

 

A little close up of the transition between the two parts

 

 

And after a quick blast on the linisher to remove the paint you can see that its not turned out too badly at all.

 

 

 

Not something I'd wish to do all the time, but an interesting exercise none the less.

[lee w 118]

I've chopped and threaded more than my fair share of AI barrels over the last 2 years, but this is the first time I've done this.

 

Customer wanted to keep the full 26" of his new .260 Rem barrel, and the M18 x 1.5 Standard muzzle thread, but didn't want to have the 23mm long AI spigot on the end of his barrel.

 

Initially I was asked If I would re-profile the blank to blend the spigot in to the rest of the barrel, this would have worked, but seemed overkill so I came up with this idea.

 

I Mic'ed up the existing spigot at 22.80mm, then turned and bored a sleeve from a piece of AI .338 barrel I had lying around from a 20" chop down. I made it 0.04mm smaller in diameter than the spigot. Quick burst of heat on the sleeve, some welding gloves and a trip to the hydraulic press, and we had a shrink fitted oversize sleeve on the existing barrel spigot.

 

 

Next the barrel was dialled in off the grooves to within .0002 as usual and crowned with the AI 11mm recessed crown. I also trimmed the excess material from the face of the sleeve and refaced the existing thread shoulder by approx .005 to clean it up.

 

 

 

 

 

As you can see from the pictures the sleeve was basically a seamless fit to the barrel. With only the slight variance in steel metallurgy giving it away (the .260 is a Lothar Walther, the .338 donor piece a Border)

 

Next step is to dial in the OD of the barrel as this is the feature we want to blend in to, and all operations requiring concentricity to the bore have been completed.

 

 

Then its time to remove some material from the sleeve OD in preparation for tapering. At this stage I also make sure my tool wear offset is Johnny on the spot by cutting to a non-critical oversize dimension and checking the actual dimension versus the programmed value. In this instance I made a correction of 0.037mm in the control to get the tool back on the money.

 

 

 

A couple of measurements and a little bit of trigonometry later tells me that the taper of this barrel is .464 degrees, combined with the measurement at the barrel shoulder, and I can calculate the required chamfer to blend the sleeve into the existing contour.

 

 

 

Heres a video of the lathe roughing and cutting the taper.

 

 

 

A little close up of the transition between the two parts

 

 

And after a quick blast on the linisher to remove the paint you can see that its not turned out too badly at all.

 

 

 

Not something I'd wish to do all the time, but an interesting exercise none the less.

Tidy job paddy well done

[Ronin]

Super job Paddy.

 

 

Damn you and your expensive "magic" machines

[Rob Dhu]

Black magic to me

[The Gun Pimp]

Nice job.

[Swarovski1]

Vorsprung deurch technique

[Scotch_egg]

Engineering aside. Why?

 

Must have cost a small fortune.

[1971silversurfer]

Interesting piece, potentially there is a future sideline industry in thread converters too , should it be cost efficient to process by these with CNC. This could enable the sharing of moderators/brakes on different rifles...and utilise some of those scrap barrels.

[gbal]

Vorsprung deurch technique

Pretty good- "technik" would have grossly undercredited Paddy's enginewity and skills.

 

You're ready for the Bisley Bible !

 

(I had another look,and HME seems to be described with two Joule levels (4500 and 7000) but whatever applies in the particular case it is clear enough each time! (it gives fps and ft lb too).Being a (ballistic) atheist,"the things you are liable,to read in de bible,well,dey ain't necessarily true."...but something gives on HME at Bisley,and of course other MOD ranges,

and anything above the lower value needs special treatment (sighting in and so on-I imagine this might vary,just as Bibles do....I don't have a Bisley members tie,having had an alternative education outwith the english public school system (Vorsprung durch merit).

:-)

[Swarovski1]

After a text I found out a 7mm wsm is hme, was very surprised at that, I knew the fps wernt above 3280fps but I had no ideal flbs were over the limit, hadnt gave it any thought, I knew 300wm was hme

[gbal]

After a text I found out a 7mm wsm is hme, was very surprised at that, I knew the fps wernt above 3280fps but I had no ideal flbs were over the limit, hadnt gave it any thought, I knew 300wm was hme

W areway off topic here-my fault-but you ae perhaps coming into HME the wrong way-IF you look at the Bisley regulations-not some unidetified "text" then you will see no direct reference to cartridges-that is because HME is defined in terms of MV and ME (3280 fps and 3319 ft lb,or elsewhere 5160 ft lb).It is misleading to say 7WSM is/not HME-some commercial loadings do not exceed 3280 fps and 3319 ft lb(none come near 5160 ft lb).

300 Win Mag commercial loadings don't exceed 3280,fps except for the Fereral 130 Barnes loading (3500fps);but most do exceed the 3319 ft lb limit (three 150 g loadings do not-Fed/Speer,and two Hornady the BTSP and Interbond,nor does the Rem Managed Recoil load).

 

It helps to keep things accurate-HME is not legislated/defined as calibre or cartridge-with the notable exception of a wholescale ban on 338 calibre on safety grounds.

Some texts are more definitive than others-as I suggested,things that you are liable to read in some bible,they ain't necessarily so-and the same goes for forums. Bisley has some general credibility.

Proof may be on the shooter of course.....and the safety oriented assumption may be that a cartridge is HME-not altogether unreasonably,if it might well typically be so. Be prepared.

 

But back to spigots,I think,please.

gbal