Installing Front Sight Base on M1903A1

[jwynne]

Newbie to the forum here.....
I acquired a couple of years ago a Springfield M1903 that has the rear base installed for a Unertl 8x scope, but not the front. I bought a set of bases from Steve Earle and a C-stock, and I want to convert it to a CMP legal 1903A1 USMC Sniper for the Vintage Sniper matches.

So, I need to mount the front base. My question is - what is the thickness of the barrel 7-8" forward forward of the breech end?

The front base mounting screws protrude about 0.140" from the bottom of the block, so allowing for the drill tip, I'm looking at drilling about 0.200" deep into the barrel. I want to make sure I don't drill into the bore, and that I leave enough metal there to keep the gun safe, while also getting enough thread depth to be secure. Am I okay drilling this deep, or do I need to shorten the screws?

Thanks in advance for the help!
John

[rcathey]

Use a pair of calipers to measure the barrel diameter at that point. Subtract .308 and divide by two. That’s your thickness.

Sounds like a fun project! I love those old long tube scopes.

[Herschel]

rcathey's instructions will work but I have a quicker answer. From a chart from Lyman showing the application of sight bases for various firearms,
they show a front base having a height of .475" from the top of the base to the center of the bottom of the base. The bases (called blocks by target shooters)
are listed as a Lyman O and Lyman E. Even though the scopes and mounting assembly are commonly referred to as "Unertl type", Lyman was using
them years before Unertl came on the scene. The chart shows the bases on 6" centers. To get 1/4 minute clicks on the sight they should
be mounted on 7.2" centers. The chart shows the same blocks for the 1903 NRA Sporter and the 1922 series (.22 cal) as for the issue
1903 even though the barrels of the Sporter and 1922 are slightly thicker than the issue 1903 barrel. I suppose the slight difference could
be dealt with a few more clicks of elevation. Setting all the detail aside, the quick answer to your question is .475" height for the block you need.

[rcathey]

I don’t think he was asking for the height of the block needed but the thickness of the barrel underneath the block.

But either way, there’s some great info in this thread now!

[jwynne]

The (diameter - 0.308) / 2.... Why didn't I think of that???? Anyway, thanks, rcathey for the great tip! And Herschel, thanks for chiming in on the base heights. I actually ordered a set of Steve Earle's "O" and "E" bases - he makes them in standard height, 0.1" taller, or 0.2" taller. I ordered the 0.2" taller bases as a friend of mine found it gives a little better bolt clearance. The Hi-Lux scopes comes with bases, but the Steve Earle bases are worth the extra $50 in my opinion. And everything I have read is that the bases need to be 7.2" apart, center-to-center, or the turret adjustments will be off. Thanks, all, for the great info.

[ed skeels]

James Root (Rootsy) has a in depth article in the CMP forum on building a USMC style sniper. Its from chasing parts to load development. Really great read and time saver.
Ed

[jwynne]

Ed, thanks for pointing this out to me - it's a fabulous article! I had found something similar when I did my faux Lee-Enfield sniper build, but there is precious little to be found on the internet about the details of assembling a USMC type sniper rifle. My Google search had not found the James Root article, but knowing it was on CMP and the author's name took me right to it... And the info on barrel replacement may come in handy as well in the future. There is a video on YouTube for installing the scope bases that is pretty good, but it's got some errors in it (which he corrects), so it's valuable as much for knowing what not to do, as what to do... Thanks, again!

[Herschel]

Honestly, I mis-read what the original question was. Sorry to take up space with un-needed information.

[jwynne]

Herschel - with me being new at this, all information is needed! Thanks for helping!

[rcathey]

Agreed! I didn't know that Lyman had those bases figured out before Unertl. Neat info!