7.62mm US GI M1 Garand Barrels

Research Project: Their Port Sizes

For years I had heard about two different gas port sizes on the M1 Rifle's Springfield Armory 7.62mm barrels.  When inspecting barrels at gun shows it was difficult to distinguish port sizes without a comparison.  I started carrying the muzzle end of a demilled Cal. .30 Garand barrel with me for use as a comparison.  All 7.62mm barrels I saw had gas ports larger than the 30 caliber barrel’s port. I had not run into the SA 11686514 Barrel yet, so there was a lot to learn.

Then I discovered a strange new technology called the inter-net.  Everything suddenly was at my fingertips.  What a great method to test the theory of the different gas ports. 

Many message board members had been posting all sorts of information about markings, heat lots, and various other facts.  Nobody seemed to be speaking about the different port sizes found on the US GI 7.62mm barrels.  I made a few posts on the Gun and Knife and Culver Boards asking for input.  Within a couple of days I had a fairly good base of information to add to the inspection list from gun shows. 

In June of 2002  I consolidated the information onto a spread sheet dealing with port sizes. I stayed away from the sleeved barrels; this information is applicable only to US GI barrels manufactured with 7.62 chambers.  Not included in this study were the two 1950 manufactured SA T-35* barrels chambered for the T65-E3 cartridge.   The T65 series of ammunition dates back to 1944 and too many different powders and charges were tested over the years.  I wanted to stick with gas port sizes that would handle 7.62mm ammunition produced after standardization in 1954.  The barrels studied were Springfield Armory production, Springfield for H&R, Springfield for AMF and I eventually added the RIA production from 1969.  Some barrels were marked SPL, others were not. 

                                                   Port Sizes Found During Study

Part No. & Date    

Qty Viewed

 . 0790+.0015



SA 11010457   5/65

Approx 35



SA 11010457   5/65     




SA 11010457   9, 10,  12/65




SA 11010457  9/65 SPL





SA 11686514   3/66




 RIA 11686320  1969 SPL  M118





Summary:  So far I have found only two SA 11010457 that exist with the Cal. .30 gas port.   This leads me to the belief that SA 11010457 was originally produced with this small gas port. The majority were then modified to .1065 sometime after September 1965.   The September of 1965 example is marked SPL, the May of 1965 is not. Future data may change these results.  My gratitude goes to everybody who submitted information, and I thank every one of you.

I know this will generate many questions which I will not be able to answer.  One thing I noticed in this study is the SPL marking seems to have no obvious meaning that I can prove.  Any definition on the SPL marking, by me, would be speculation.  It was just too random in its application.

The picture below shows ports according to size, not by timeline. ports combined finished Left:  Small Cal. .30 Port (.0790+.0015) as found on all Garand barrels 6535448.
Middle:  Smaller Enlarged Port
(.0995) as found on Rock Island Barrels 11686320 from 1969,
Right:  Largest Port (.1065) as found on mostly all of the Springfield Armory 11010457 from 1965, and all SA 11686514 1966 production.

7.62mm combined fin Excluding the T35 series, these two barrels are some of the earliest 7.62mm barrels produced at SA. The top barrel is dated 9/63, Y37 heat lot, P&M, no DAS.
The bottom barrel is dated 9/64. Its heat lot is BU14, P&M, with DAS. Both barrels have the smaller Cal. .30 gas port size, and are pre-drawing number assignment. The 1963 was probably used in a test.  The later one was probably one of the chambered barrels for comparison with the sleeved barrels, a test done at SA during the fall of 1964.

I am still looking for information on the following:


Any 11010457 barrel dated earlier than 5/65 or later than 12/65


Any 11686514 barrel with a date other than 3/66


Any 11686514 barrel with an additional digit, making it 9 digits long.  I had two reports
and should have paid better attention.  I now regret that I dismissed them as typos. They probably are production errors and do exist.

*I am paranoid about the use of dashes in military designations.  Wouldn't you know it, Bob Seijas made a friendly point to show me that the T35 barrels in his possession are both marked T-35.  Bob's witty email said "Note the dash in the nomenclature":>). 

A short time later I purchased a T-99E3 Grenade Launcher.  So much for my paranoia.

This information may be used by anybody.

All inquiries regarding this research project must be by email.