A1 Low Velocity

Clues · 01-13-2020, 03:34 PM

I recently bought an A1, rebuildable ram, magno valve.

I've had an awful time trying to get this thing to chrono over 230, often times its sub 200. Velocity adjuster all the way out, no real velocity change. Previously I was dealing with a ton of bolt stick and so I got a rebuildable ram for it which I expected would solve the problems, it has not.

I bought the HPR Gauge and a standard stem to use it. Without making any other changes I used the standard stem, plus the HPR and LPR gauges and suddenly the thing is firing correctly, 270-290 FPS at 300+-20 HPR PSI. The LPR is between 55-60 PSI.

I played with it a bit with the HPR gauge installed because I don't have a standard valve stem guide cap and it played pretty well, still a little bolt stick though
(Dr. Strangelove, you said previously that the rotobreech gasket's glue would expand and cause friction between the rotobreech and the bolt, that might be my bolt stick issue)

So I'm wondering what the next step should be, I'd like to use the magno vale I have, but without the standard stem I cannot get any velocity increase even at 400+ PSI. Which leads me to believe its got something to do with my magno stem / ram head. Is it possible I'm not getting a full valve opening somehow and so really no matter how high the HPR pressure its I just don't get enough air behind the ball? I'm at a loss.

twinings · 01-13-2020, 11:47 PM

I’m also struggling to get an A1 working. And had low velocity problems. Maybe check the shim stack in her HPR is correct and raise the LPR pressure?

Clues · 01-15-2020, 01:46 AM

The HPR seems totally fine, the HPR gauge readings are right in line with what I would expect and the LPR should be fine for magno, especially considering it pushes the standard stem back no problem.

Looking at the magno stem its a few mm shorter than the standard stem, which reminds me of this old thread. I guess they were generally short but compatibility was a problem which doesn't give me a ton of hope that I can solve this easily.

The bolt is already pretty forward when the ram is in its engaged-rear position so I don't know what else I could do to lengthen the ram stroke since moving the ram head any further will make it impossible to fit the bolt.

Clues · 01-15-2020, 07:27 PM

Talking with a few other guys it was brought to my attention that the magno valve guide and the standard valve guide are NOT the same. In fact the standard valve guide is not compatible with the magno system! Which might be the issue I'm looking at. Does anyone know what the visual differences of the two valve guides are so that I can determine which one I have? It looks like the magno guide has that large white bumper on the rammer side that isn't present on the standard guide?

Clues · 01-15-2020, 07:32 PM

To continue the great work of those around me I'll include the photo of the magno guide vs. standard for anyone else who might need it.

th3p0stm4n · 01-19-2020, 04:45 PM

Are you on the FB group?

Clues · 01-20-2020, 10:41 PM

Yes; I can post over there at this point

dr.strangelove · 01-24-2020, 02:05 PM

Quote:

Originally Posted by Clues

It looks like the magno guide has that large white bumper on the rammer side that isn't present on the standard guide?

That is correct. That's probably the root of your problem.

Clues · 02-18-2020, 01:41 PM

To close the loop here it was the magno stem, as it always seems to be.

The velocity would actually get worse as I turned up the HPR pressure since the cup seal had gotten loose from the metal stem and the HPR pressure would keep the cup seal semi-forward while the metal stem moved when hit by the ram.
It wasn't obvious at all as the cup seal didn't seem free of the stem, and every time I pulled the stem out the cup seal was tight and back where it was supposed to be. Until finally last weekend it came out totally disconnected and everything fell into place.
Some JB Weld locked the cup seal in place and the A1 *finally* starting shooting 300 fps with the magno. Its not totally dialed in but its now actually serviceable!

The other issue I had was bolt stick, which can be its own complicated solve. Mine specifically was odd because additional shots would oftentimes reset the bolt correctly, which in hindsight seems like a good indicator that the solenoid is having trouble. I pulled the solenoid out and found a decently sized piece of foreign material on my solenoid stem, which would certainly could cause it to jam forward. After cleaning that out I haven't seen the issue reappear but I don't think I've put in the shot volume to confirm that fix just yet.

dr.strangelove · 02-18-2020, 02:55 PM

You may want to check your mini-reg assembly. A lot of the time if there's a foreign material in the solenoid, it's bits of o-ring from the small piston.

EastCoastAngel · 02-22-2020, 10:38 AM

I had a a1 that came in and the valve stem was a magno unit and the valve guide was a stock part. because there is a length difference it wasnt allowing the valve stem to open up all the way and would only shoot low 200s. match the valve stem to the valve guide. magno will have a valve guide with a white bumper on it. and you will notice you dont have to run the hpr through the roof to get that 275-280 fps.