Printable View
I am wondering what was the typical MW/TE on new production M1917 barrels. I currently have 3 M1917's; an Eddystone 1,277,XXX bbl 11-18 MW 2.75 TE- 4.0 (no rebuiild marks, pitted bore), Remington 279,XXX bbl 7-18 MW-2.5, TE-3.0 (O.G.E.K. nice bore) and a Winchester 321,XXX 6-18 MW-2 TE-3.0 (original, no rebuild markings, perfect bore, SA 131 stamped on buttplate). These barrel readings seem appreciably higher than my assorted M1903's of the same age/condition. Observations/comments?
Fred
There are two GI Breech Bore (erosion) gages with drawing #C3940. One has nine spaces between the rejection line for machine gun barrels and the rejection line for rifle barrels, the other has eight spaces between the two rejection lines. (IIRC the 8 space one was a mistake, but they still used it) So,, if you have the one with nine spaces,, the rejection point for the M1917 is 0.309” and if you have one with eight spaces the rejection point is 0.0310”. (The M1917’s receiver is slightly longer than the M1903’s.) Your barrels are no where close to the rejection point of either gage. But I would say that when new and if the barrels were made to the published tolerances,, a new reading would be 0.301” with the nine space gage and 0.302” with the eight space gage.
These Breech Bore Gages were made to the specs of the pre-WWII bore/chamber dimensions.
IIRC, the loosening of .30 cal chamber and bore tolerances occurred in early 42.
Example: very few new M1903 WWII production barrels measure any less than 0.302”. Ive only had the opportunity to measure a few new (or close to new) pre-1940 barrels and they ran about 0.301” or less.
There were warnings in the “Ordnance Sergeant” that this relaxing of tolerances should be taken into account when taking breech bore (erosion) readings.
Your barrels all sound good as regards to throat erosion.
As to muzzle wear, with the M1917, I would first determine what the grove diameter is before I could get a understanding of the MW gage reading . WWI production barrel do have some manufacturing variations. With a five grove barrel,, determining grove dia. by slugging can be a problem. However with a good caliper, a very good approx. can be made. (I use a V block, a depth mike and pin gages when I measure a slug from a five grove barrel). What ever that grove dia. measurement is, it should not extend to the rear of the end of the bore by more than ¼”.
The readings you give with your WWI production barrels sound very good to me but unless you know the grove diameter with each barrel, you really can’t determine what the “NEW’ reading should be.
I haven't gotten around to buying a mw guage yet but I did a comparrison of my rifles and some barrels I had using the bullet test and a set of calipers.
Two winnys with original barrels, .171 and .144. Remmington .168. Eddy .185. Eddy takeoff ? barrel dated 11-18 .198. New HS .170. JA takeoff barrel .178.
The cartridge used was korean surplus.
John
45B20 & jamie5070-
Thanks for the interesting and useful info on M1917 barrel specs. I've been using my CMP muzzle wear gauge and an Ara-Mor throat erosion gage (it comes with spacers for 30-06 bolt, m1 30-06 and m1/m1a .308). Its scale goes up to 9 with the next mark being "reject". I had no idea that how a barrel was rifled would affect the reading on a muzzle gage. I have two essentially new pre 1940 SA barrels, one a star gaged 3-38 on a NM 03A1 and the other a SA 1930 that I had put on a 1.4 mil CMP receiver in a Keystone C stock. They both have TE less than .5 and MW of 0. Given my lack of patience and technical skills, I am happy to accept your experience and expertise.