@SanginSpecial - it was not directed to anyone in particular. it was a question for others more knowledgeable than me.
thank you for your answer. it makes perfect sense to me. i agree that $650 is alot of money for something to not be close to ideal.
with that in mind, i have seen several posts from Area 419 about this and the Bartlein drop-ins are headspaced at .043 or .044 and they are saying that is acceptable for nrl22 / rimfire prs. do you think that could push an action out of saami spec?
MD.. SAAMI spec for 22lr headspace is .043" to .051". With that said, Area 419/Bartlein is within spec. The thing to remember about SAAMI specs is that they are a saftey first spec. As a business, Area 419 has to keep their rear covered, so they are obviously keeping headspace in the tightest end of spec. .043 to .044" will probably shoot quite well with Lapua/SK ammo since the rim thickness is .043". IME, .042" to .043" would allow for better accuracy potential, but for liability reasons, no drop-in manufacturer would likely ever go that tight. I can see how Area 419 can claim the lower end of the SAAMI spec, since they are custom building rifles. Proof could never claim that tight of headspace for CZ's with a barrel tenon at 1.189". With the variences in receiver/bolt depth on CZ 455 and 457 models, their headspace could potentially be anywhere from .044" to .049" based on the receivers I've measured.
Here's a glimps into my testing with some R50. The rim thickness of R50 is .041". I shot 5 groups of 5 shots and averaged them for comparison of varying headspace dimension. This testing was done at an indoor range off of a rest and rear bag. (Not optimal ammo for the rifle as far as lot testing goes. But, all testing was performed with the same lot in order to keep the playing field level.)
Headspace/ Group avg.
.039"/ .479"
.041"/ .390"
.042"/ .448"
.043"/ .567"
As you can see from this example test, just .002" of increased headspace had a dramatic effect on accuracy, and the tightest group average correlated with the ammo's actual rim thickness. I've since repeated this test several times with various ammo/lots, and each time I get the same result, headspace matching rim thickness gave the tightest groups. This particular test didn't cover .001" tighter than the ammo's rim thickness, but in other tests, it is very close to matching the results of headspace matching rim thickness.
I've kind of strayed off the original topic of the thread, but it was a good opportunity to attempt to warn folks of the pitfalls of headspace as it relates to drop-in barrels. I really hope that Proof listened to what I shared with them. They probably have a nice product, but it could be so much nicer if they'd finish the race, so to speak.
