In a recent thread, it was suggested that the rubber powder/shot seals used in the Hornady 366 measure casting assembly were available from McMaster Carr in bulk at a very good price. MMC calls them "square O-rings."
I did a little research on the original MMC part # that was provided in the earlier thread and found that it was close, but not correct. If you order by that part # (4061T-234), you will get O-rings that are too big. The correct part # is 4061T-23 and was confirmed via PM with the original poster.
A few days ago, I ordered a pack of 50 square O-rings from MMC (part # 4061T-23). They arrived today and I have checked them out pretty carefully. While they are ever so slightly thinner than the new Hornady parts I had on hand, I think they should work fine IMO.
The Hornady parts I had mic'd 0.135" to 0.137" in thickness. The MMC Part # 4061T-23 consistently mic'd 0.132" thick. I don't think the 0.003-5" difference will be significant as I mic'd a couple of used seals that were still functioning properly at 0.130".
The OD and ID of the Hornady and MMC seals appear to be the same and both fit snugly in the measure casting assembly, as they should. Trying to mic the OD and ID of a flexible rubber O-ring is a study in futility, so I didn't bother. I just relied on the feel of the fit in the measure casting recess. Both fit snugly. I do suspect that the snug fit actually increases the "apparent thickness" just a bit, due to compression. Both felt just slightly proud of the surface of the measure casting assembly; again, as they should.
The Buta-N material in the MMC "square O-ring" felt just slightly stiffer than the material in the Hornady part, but I have no real way to confirm that. I do not know the composition of the material in the Hornady part; it may be Buta-N as well.
My overall impression is that they should work just fine. At about $0.27 each ($8.07 + $5.32 for shipping = $13.39/50; $0.2678 each), they are certainly a lot cheaper than the $2 or so each that Hornady and other suppliers charge.
I did a little research on the original MMC part # that was provided in the earlier thread and found that it was close, but not correct. If you order by that part # (4061T-234), you will get O-rings that are too big. The correct part # is 4061T-23 and was confirmed via PM with the original poster.
A few days ago, I ordered a pack of 50 square O-rings from MMC (part # 4061T-23). They arrived today and I have checked them out pretty carefully. While they are ever so slightly thinner than the new Hornady parts I had on hand, I think they should work fine IMO.
The Hornady parts I had mic'd 0.135" to 0.137" in thickness. The MMC Part # 4061T-23 consistently mic'd 0.132" thick. I don't think the 0.003-5" difference will be significant as I mic'd a couple of used seals that were still functioning properly at 0.130".
The OD and ID of the Hornady and MMC seals appear to be the same and both fit snugly in the measure casting assembly, as they should. Trying to mic the OD and ID of a flexible rubber O-ring is a study in futility, so I didn't bother. I just relied on the feel of the fit in the measure casting recess. Both fit snugly. I do suspect that the snug fit actually increases the "apparent thickness" just a bit, due to compression. Both felt just slightly proud of the surface of the measure casting assembly; again, as they should.
The Buta-N material in the MMC "square O-ring" felt just slightly stiffer than the material in the Hornady part, but I have no real way to confirm that. I do not know the composition of the material in the Hornady part; it may be Buta-N as well.
My overall impression is that they should work just fine. At about $0.27 each ($8.07 + $5.32 for shipping = $13.39/50; $0.2678 each), they are certainly a lot cheaper than the $2 or so each that Hornady and other suppliers charge.
