Yeah the last time the Marines received new service rifles was about 1918. In 1919 they received barreled receivers, but not complete rifles. After 1918, the only complete rifles they received were the National Match rifles. Which were very small in number.

In the 1920's they did get some more barreled receivers, swapping a likewise same amount of barreled receivers back to RIA. I think this is where all those high number RIA's came in personally.

The Marines stopped receiving loose barreled receivers about 1927, and after this date did not get any different receivers until the Navy sent at least 35,000 and possibly up to 50,000 in early 1942.

But the docs detail the Navy rifles were basically the ones that the Navy had used and abused in training and they all needed rebuilt.

I think if I remember right it elludes these were the rifles that were used to train recruits at a training facility such as the Great Lakes or something like that, and the Navy was like we don't need rifles that can shoot to train our men, so they freed them up for the Marines.

The most logical way a 1.51 could have came into the Marines was as a NM. But even that it is very unlikely as there was a break of when the Marines bought new National Match rifles, and there was a controversy that happened in 1928 that would make it very unlikely the Marines would have got a 1.51 serial range in any of their NM shipments.

It's sort of a longer story than this cliffnote version, but it's so rare to find any Marine rifle above the 1.03 serial range.

Honestly the Navy rifles that I've seen serials on were usually WWI or earlier serials as well.

But I mean it sort of makes sense on why this would be when you think about it. The Army only produced receivers past the early 20's, to swap with their low numbers they were rebuilding. They didn't produce receivers to build new rifles other than the NM or sales rifles.

So that is why I have always thought you really only see WWI or earlier serials in the Marines and Navy. Because all the higher serial ranges the Army was making were going internal to swap with their low number receivers on rifles going in for rebuild