i replaced the barrel of my M1A to a heavy match barrel made by douglas. my gunsmith told me that the barrel headspace is milspec. if i'm right or correct me if i'm wrong that the barrel headspace now is like a stock barrel? so its fitted like a stock barrel, no longer a match fit bec. its a milspec fit. will i'll be loosing the accuracy of a match barrel? i would appreciate very much any info you can provide. tx for your time............
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headspace question
- Thread starter carlos velez
- Start date
"...barrel headspace..." Barrels don't have headspace by themselves. Headspace is a tolerance between the bolt and chamber. You won't be losing any accuracy. Work up a load(using milsurp or factory will be a waste of time) and go shooting.
Headspace M1A
The only way to determine headspace is to measure it with the appropriate headspace gauges.I'm assuming that you have a .308 Win chamber,not a 7.62 NATO chamber which is longer.For the .308 Win the minimum or "go" headspace measurement is 1.630,although it is best practice to cut the chamber to 1.632 in a semi-auto as a safety precaution to allow for accumulation of chamber fouling.The "no-go" meaurement for the .308 is 1.634 and the "field" or safe limit is 1.638. The 7.62 NATO is a bit longer.I just finished building a Garand with a military 7.62 barrel and installed a bolt which allowed the 1.634 "go" gauge,but did not allow the 1.638 "field" gauge,which I consider a "no-go" for the 7.62.The bolt will not close on the 1.634 gauge with .002 shim stock on the base of the gauge,so my actual headspace is approx 1.635.You should talk to your gunsmith,and perhaps get him to re-gauge the chamber and tell you what the headspace actually is.As long as you are within the 1.638 "field" limit your rifle is safe to fire and I don't think any real difference in accuracy will be apparent.
The only way to determine headspace is to measure it with the appropriate headspace gauges.I'm assuming that you have a .308 Win chamber,not a 7.62 NATO chamber which is longer.For the .308 Win the minimum or "go" headspace measurement is 1.630,although it is best practice to cut the chamber to 1.632 in a semi-auto as a safety precaution to allow for accumulation of chamber fouling.The "no-go" meaurement for the .308 is 1.634 and the "field" or safe limit is 1.638. The 7.62 NATO is a bit longer.I just finished building a Garand with a military 7.62 barrel and installed a bolt which allowed the 1.634 "go" gauge,but did not allow the 1.638 "field" gauge,which I consider a "no-go" for the 7.62.The bolt will not close on the 1.634 gauge with .002 shim stock on the base of the gauge,so my actual headspace is approx 1.635.You should talk to your gunsmith,and perhaps get him to re-gauge the chamber and tell you what the headspace actually is.As long as you are within the 1.638 "field" limit your rifle is safe to fire and I don't think any real difference in accuracy will be apparent.
Headspace M1A
It is correct that headspace gauges are intended to verify that a chamber is within functional tolerances for a particular cartridge.The gauges can, however,be used to get an indication of chamber length as they are precision ground to a known length.With a gauge for a rimless cartridge like the .308 Win,the length of the gauge is established from the base of the gauge to a known datum point on the shoulder of the gauge.For the .308 the "go" gauge is 1.630,the "no-go" is 1.634,and the "field" gauge is 1.638. You can actually purchase a set of 9 headspace gauges for the .308 which increase by increments of .001 from 1.630 to 1.638 and allow the overly fastidious to get a precise read on headspace. If I were checking this rifle with the standard set of 3 gauges I would begin with the 1.630 "go" gauge to verify that headspace is at a safe minimum.I would then add a disc of .002 shim stock,and then .003 shim stock, to the base of the gauge to establish where the headspace was in relation to the minimum.I would then check with the 1.634 "no-go" gauge and continue adding shim stock if the rifle accepted the 1.634 gauge.I'm a bit confused by the gunsmith's reference to a MILSPEC chamber for a .308,as this is a contradiction in terms.There is only a MILSPEC for the 7.62 NATO which is slightly longer than the .308 Win.
It is correct that headspace gauges are intended to verify that a chamber is within functional tolerances for a particular cartridge.The gauges can, however,be used to get an indication of chamber length as they are precision ground to a known length.With a gauge for a rimless cartridge like the .308 Win,the length of the gauge is established from the base of the gauge to a known datum point on the shoulder of the gauge.For the .308 the "go" gauge is 1.630,the "no-go" is 1.634,and the "field" gauge is 1.638. You can actually purchase a set of 9 headspace gauges for the .308 which increase by increments of .001 from 1.630 to 1.638 and allow the overly fastidious to get a precise read on headspace. If I were checking this rifle with the standard set of 3 gauges I would begin with the 1.630 "go" gauge to verify that headspace is at a safe minimum.I would then add a disc of .002 shim stock,and then .003 shim stock, to the base of the gauge to establish where the headspace was in relation to the minimum.I would then check with the 1.634 "no-go" gauge and continue adding shim stock if the rifle accepted the 1.634 gauge.I'm a bit confused by the gunsmith's reference to a MILSPEC chamber for a .308,as this is a contradiction in terms.There is only a MILSPEC for the 7.62 NATO which is slightly longer than the .308 Win.
