Headspace problems

[stanlyonjr]

Here's one for you reloading experts out there. I have an AR-15 match service rifle. I reload to the headspace spec using a Wilson case gauge. It seems no matter how much or less headspace there is I get blowby around the case. Everything is measured to saami spec. Is that just the nature of the AR-15 and other gas guns?

Stan

 

[Steve Blair]

Sounds like your loads might be a little mild and not properly obdurating around the neck.

 

[stanlyonjr]

Thanks for the reply Steve. For the most part my loads are pushing max if not at max esp. when shooting at the 300 and 600 yard line. I have measured my chamber and it has an overall length of 1.780 as opposed to the saami spec of overall length of 1.750 to a max of 1.760 for 223 rem. I'm not sure if that has anything to do with anything I'm talking about. According to the instruction that came with the Wilson case gauge, you only need to size back .002 to .003 thousands. That would be out of saami spec according to the gauge. I have not tried it. Any thoughts?

Stan

 

[fdshuster]

Stan: I have not used my Wilson case gauges in years: no longer have a use for them since I began using the Stoney Point/Hornady chamber Over-all-Length gauge to measure the headspace lengths of every one of my chambers. The Wilson (and other types) will assure that your cases are withing SAAMI specs, but with that there are still plus and minus tolerances involved, so you are getting a "general" indication, not exactly what your chamber is. For my AR's I take a headspace length measurement of the case as it comes out of the chamber, after punching out the primer, and that measurement is 1.459" (on one of my uppers). The sizing die body is adjusted to push the shoulder back to 1.456", guaranteeing positive chambering every time. Varmint bolt guns will have the shoulders pushed back .001" or .002", and with the benchrest chamberings the headspace length will remain the same as fired. Your chamber over-all-length of 1.780" is pretty much the standard letting cases stretch well beyond the maximum length of 1.760" and still remain "safe", for those who do not monitor case stretching and the need to occassionally trim back to 1.760". If by "blowby" you mean the carbon buildup on the case necks after firing, I also get that, to a greater degree when using the dirty ball powders as opposed to extruded/stick powders.

 

[GermanS1]

Stan, AR15's leave cases looking very sooty as a result of the gas system's method of operation. When the bolt carrier moves back and disconnects from the gas tube, there's a significant volume of carbon-filled gas blown into the loading port area where the newly fired case comes out. They get a good coating and look nasty compared to something fired from a bolt action.

As for setting the headspace back, 0.002" to 0.003" less than the fired cases will be enough to ensure reliable function in your upper as long as the base is also being sized properly. If it isn't, you won't have any doubt because the bolt won't open at the shot, you'll have to do it manually.

 

[stanlyonjr]

Sounds good guys thanks for the reply. I'll try those techniques and see what happens.

Stan