Is .750 behind the gas block thick enough for an spr?

[Qazwsx]

That’s the question. 18”, mid length +1 with a 1/8 twist that would live its life eating 262 and hornady 75gr. Enough for 10-20 round stages or no? My 18” jp that’s .65 under the handguard opens up too quickly.

 

[drewthebrave]

I mean, are you building a true Mk12 SPR, or just an SPR inspired build? I'd argue that the quality of the barrel is more important than the diameter under the handguards. I can't seem to find the official drawing for the profile, but I do remember it was 0.840" or 0.850" under the handguards. I'm not sure how much weight you'd save going down to 0.750", but the original profile SPR barrel weighs about 2.5 pounds. Since you already have the light profile JP, I'd recommend going for the true SPR profile barrel from Compass Lake or have a custom Bartlein/Krieger/Lilja turned to at least 0.840" under the handguards just to be safe.

 

[Qazwsx]

Don’t care at all about clone correct. More due to availability of white oak and compass lake right now and wanting 1/2x28 for a can where most 20” tubes are specd 5/8.

 

[drewthebrave]

Then take a look at Craddock Precision. He can customize it to your specs.

 

[Slevin182]

If it was me I'd go with a bit thicker. Pretty sure the SPR barrels from WOA are .850 behind the gas block. Won't go wrong with one of them, and will go a 20 round stage.

 

[TonyTheTiger]

What are your accuracy requirements? 10-20 rounds shouldn't be changing much at all. Can't count the number of times I've seen that JP profile burn through most of a D60 then do great on 3 ish moa targets out to 500 yards. Done it plenty myself with similar barrel contours. Never had to shoot anything like a 1 moa target at the end of a barrel burner stage though.

 

[Qazwsx]

Opening up from .75 moa or less to 1.5 isn’t as big of a concern as an upward shift of 2+ moa

 

[PlinkIt]

Opening up from .75 moa or less to 1.5 isn’t as big of a concern as an upward shift of 2+ moa

Perhaps I'm in left field...
Upward shift would be either stress showing under heat
Or rounds getting hot / faster from sitting in the hot barrel for a moment then showing up at distance as high from extra speed

Would it not?

 

[Qazwsx]

Not sure what causes it but it’s present on my jp and some other lighter profile rifles.

 

[j-dubya]

Perhaps I'm in left field...
Upward shift would be either stress showing under heat
Or rounds getting hot / faster from sitting in the hot barrel for a moment then showing up at distance as high from extra speed

Would it not?

You are correct. Primarily stress in the barrel.