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Mentolio · Veteran Member

This Christmams I finally bought an American Classic 1377. Initial Chrony testing looks good (averaging in the high 500s-low 600s with RWS Super H Points at 10 pumps), and grouped well enough, though I couldn't adjust the rear sight near low enough to get my pellets "on target

Last week I ordered some goodies from Alchemy Airwerks, and put them on this weekend...major difference! Adding the shoulder stock allowed me to use the rear peep sight, and made shooting far more stable. I also added the 2289 fore grip, which REALLY makes the gun easier to pump than the new style "slim" fore grip. Lastly I installed Alchemy's stainless pivot pin. Gun still shoots a little high, but otherwise is great!

I can't believe I waited this long to get one of these guns! Though I haven't Chrony'd them yet, this gun shoots H&N Terminators very accurately out to 20 yards.

I plan on doing the "usual" mods: left handed breach, 18" barrel, larger transfer port, and a flat top piston and valve combo. I read RSterne's study on stock vs. adjustable vs. flat top, and know that flat top is the way I want to go...which brings me to my question for the experts: what kind of flat top piston is best, and why? I don't mean "whose" or "which company's" piston as much as which design? I've seen adjustable "760" flat top Pistons with what I assume is the stock seal and oil wiper, and I've seen a few that appear to use one or two Orings to seal. Which design is better and why?

Mentolio · Veteran Member

Been a few months, and just read the previous post. I originally posted Chrony results of high 700s. Boy, that would be nice! The gun did every bit of 600fps with RWS Super H Points @ 10 pumps, maybe a bit higher, but not 700! Sorry...

Anyway, since that post I have tried to add a hi-flow transfer port and flat top piston and valve combo, but the seal on the piston would not build enough pressure to pump any more than 4-6 pumps. The gun wouldn't shoot over 460fps, even at twenty pumps with that setup. Thankfully, Dave @ Alchemy Airwerkz took the valve back and gave me a credit (thanx Dave!). So I applied it towards Alchemy's left handed, loaded, aluminum breech; a stock Crosman front sight, and his 3-d printed barrel band for longer barrels. So now my 1377 is a carbine with an 18" barrel. Of note about the left handed breech: it appears to use the stock bolt, which in the stock breech doesn't allow a pellet skirt to clear the transfer port completely. The new breech has different spacing, or perhaps a slightly longer bolt, which basically allows the pellet skirt to clear the port, at least it seemed to in my hastily done experiment before assembly. Nice job...

Numbers as follows (I wish I could find my original, box-stock Chrony numbers, but I think they got thrown out):
RWS Super H Point, 6.9gr pellets. 10 shot series at 10 pumps.
Low: 653.8, High: 666.3, Av: 659.9, ES: 12.49, SD: 4.24
I then did a 5 shot string at 5 pumps and got an average of 526.2, with an ES of 11.69. Then, for giggles, I did strings of 5 shots at 15 and 20 pumps:
15 pumps: Av 723.0, ES 5.78(!), SD 2.0
20 pumps: Av 758.0, ES 8, SD 3.74.

Bob La Londe · Veteran Member

domer_pyle · Senior Member

How did you get the roll pins through the pump lever? I just bought another one today and tried to put my 2289 handle on it but the pins are slightly wider OD than the threaded holes in the lever

Mentolio · Veteran Member

domer_pyle: I didn't install the pump linkage in the pump arm. I bought mine already installed.

domer_pyle · Senior Member

Ahh ok. Just figured I'd ask before drilling them out a bit. So did you just go back to the stock valve after sending the FT back? I've got a FT valve and piston on the way with a 16" barrel and the anticipation is killing me!

Mentolio · Veteran Member

Yessir, stock valve for me (for now, anyway).

domer_pyle · Senior Member

Nice, those are some decent numbers. When these parts get here this week I'll chrony it with just the longer barrel and then with the valve and piston too. Right now it's throwing Premiers at 551.8 average and the milk carton pointed at 558.? but the pointed had less than 9 fps spread, so I'm hoping those turn out to be as accurate as the Premier

domer_pyle · Senior Member

Well, change of plans. I haven't gotten the barrel yet but with the valve and piston, a high flow transfer port, and a modified stock bolt probe I'm getting about 605 with CPHP at 10 pumps with an ES of less than 5 fps,and right around 660 at 14 pumps with an ES of about 8 I think it was. Pretty excited to get the barrel and my tubing from Online Metals to make a shroud