I will always take issue with and call out people stating that it's safe to exceed design parameters or that there's no risk in using weapons with problems like excessive headspace. THR posts come up frequently in search results, and people seeking to do something questionable are often predisposed to accepting answers they want prime facie. Ergo, the responsible thing to do, the THR way, is to always acknowledge in discussing such things that they are accompanied by very real risks to the user and bystanders.
Is it not amazing the number of people who are always trying to push a weapon to its design limit? What is it with these people, why are they trying to advocate that shooters load their weapons to the edge of catastrophic destruction? Are they trickster types of personality?
Garands have not gotten cheaper over the years. I bought a bunch when they were $350, walked away when they got over $1000. I think you can still buy new HRA M1 Garands, in new wood, from the CMP. They have to be well over a $1000 now. I don't think the trickster owns a $1000 Garand, and surely is not shooting it enough to have the clip jumps, operating rod dismounts, gas cylinders loosing, stock loosing, operating rod bending issue that will come with hot ammunition. I don't want any of that, and I don't want the bolt to hit the receiver heel hard. Unless you buy a new Garand, the rest have been through one or more rebuilds. What a rifle could take for 20 to 100 rounds new, those same round may very likely cause a rebuilt receiver heel or sidewall crack.
When I shot my Garand in competition, and I shot one enough to wear out a barrel, I wanted safe and accurate ammunition. I did not want malfunctions as alibi's kill the score. Two malfunctions and you don't get an alibi. Match Garands lose their tune fast enough, the upper handguard is glued to the lower ferrule, the action is glassbedded to the stock, the operating is easily bent, and I did do bedding refreshes. For someone whose score depends on his Garand to remain in match tune, it does not make sense to slam the mechanism with ammunition the rifle was never issued, or intended to shoot.
The best policy is to stick with the bullet weights the CMP recommends, and to keep pressures low. I more or less evaluated my ammunition by how the weapon cycled. I wanted to feel the ejection, extraction, feed cycle as I shot it prone rapid fire, or sitting rapid fire. Mind you, I am shooting with a tight sling and very focused on my sights and the target. If my ammunition gave me a perceptible"clip/clop" than that was good. The weapon cycles just at the limit of human perception. If however, the ammunition cycled the weapons so the whole event is just one big bang, and the loading, extracting, feeding event was too fast for my perception, I decided that ammunition was too hot. This is not scientific, but it was one way of keeping things safe.
I roll my own as commercial ammunition was not tailored for Garands. Some ammunition companies have been offering ammunition tailored for the M1a
And you know something, you keep your 150's to the velocity on the M1a box, your Garand will run smoothly.