Here are some pump mag 12gr consistency and efficiency numbers

[Gen]

So I think I have my pump mag the way I want it. Classic valve and body, wave spring and full blue bumper, Dye barrel, Jay's pump kit, classic rail, Benchmark Groovy gripframe, CCI bucket changer and Phantom hardline. It'll be going out for anno in a couple weeks. I decided to find out what it does for consistency and efficiency on 12 grams. Here's what I came up with:

70 degrees in home. 12 gram was at room temperature. I chrono'd it @ ~275 using a 3.5 oz tank before I switched to 12 grams. Shot reballs, they fall through a .679 Freak insert. Dye barrel is 9" past end of the body in length, don't know the I.D. Interesting to find out the large difference going from a 3.5 oz to 12 grams. I'm guessing it has something to do with the available space for the CO2 to expand. Time between shots is whatever it took for me to turn and write down the number, about 6-8 seconds. Speed shown on left, shot number in parenthesis.

251
259
254
257
257 (5)
259
259
259
250
255 (10)
252
256
252
254
254 (15)
257
281
275
296
292 (20)
264
241
200 (23)
--- seemed about 150 FPS
--- went about 15 ft
--- went about 10 ft
--- went about 4 ft
--- At this point it would leak out the barrel once I pumped it.

I've found with all my markers that with the correct paint to barrel match, I'm able to shoot 10-20 FPS higher than with reballs in the same barrel. I am hoping this is the case with this marker which is why I initially chrono'd in the ~275 range. So what I'm seeing is the possibility of 22 usable shots, with the 23'rd usable to scare someone. I'm also very happy in the consistency, actually surprised.

So there you go. If you have any questions, fire away.

Thanks,
Gen

Oh yeah, pics :D

http://img.photobucket.com/albums/v185/genjuroq/PB%20markers/PumpMag-02.jpg

http://img.photobucket.com/albums/v185/genjuroq/PB%20markers/PumpMag-01.jpg

[Gen]

Well, I changed the bolt spring after seeing smoothice's suggestion to GroovYChickeN 2.0 's post here: http://automags.org/forums/showthread.php?t=226352
I now have it reliably acting as a pump without the use of a blue bumper behind the wave spring. Changing from a 50mm bolt spring to a 42mm bolt spring made it much easier to cock and reduced the likelyhood of it resetting the bolt like a semi. AND it made a difference in shot efficiency. Basically everything was the same from my test above BUT with the shorter bolt spring and for some reason, changing to 12 grams after chrono'ing with a 3.5 oz tank didn't change like before. I got more shots and at a higher average velocity.

274
279
274
278
chuffed (5)
267
268
269
252
271 (10)
272
268
268
275
265 (15)
269
270
269
272
didn't load ball (20)
283
280
289
298
287 (25)
268
252
229 (28)
---
---
---

Now I got 27 usable shots, all at a higher velocity than before. All is well, now to get it anno'd

Thanks,
Gen

Here's a pic to show my spring length compared to my bolt.

http://img.photobucket.com/albums/v185/genjuroq/tech/PumpMag-03.jpg

[rawbutter]

That's some good data! :hail:

Now I have a place to point people whenever they ask, "Just how many shots can I get from a 12 gram, anyway?"

[GroovYChickeN 2.o]

hey dude is that a stock agd spring or did you modify it? Still can't get my pump mag to work. :cuss:

[Gen]

I don't think its a stock spring. I bought it along with a couple other lengths in the B/S/T. The basic idea behind making it a pump is you have to keep the bolt from resetting, so either shim up the wave spring to make it stronger, or trim down the bolt return spring to make it weaker. I would trim the bolt spring since in my case it gave me a lighter pump stroke and more shots. If you've got an extra spring that you don't care about, just start cutting away at it, make sure to clean the end up. I think making the length of the spring the same length or a little longer than the bolt is probably a good place. At least then you'll know that there is still some pressure on the bolt.

Later,
Gen

[Gen]

Well, in an attempt to be over zealous in getting numbers, I did 4 more tests.

Test #1 - I played with it a week ago using Compressed air. It was chronoing around 280. The weather was about 50-60 degrees outside then. Didn't change anything except to put the 12 gram back in. Test was done in my office, room temp was about 70. Speed shown on left, shot number in parentheses.

293
291
299
297
297 (5)
292
284
293
290
292 (10)
287
293
290
300
312 (15)
314
305
297
294
283 (20)
284
261
257
253
242 (25)
237
225
222 (28)
---
---
---
---


Test #2 - I turned the velocity adjuster back about 1/8th turn and then adjusted as I went along to get to my target velocity of ~280. I waited about 10 minutes to let the bucket changer and hardline warm back up to room temp.

263
262
280
283
279 (5)
280
284
271
278
280 (10)
275
280
280
280
279 (15)
280
280
293
281
298 (20)
302
295
293
278
271 (25)
249
234
206 (28)
---
---


Test #3 - Done adjusting the velocity, another test.

267
261
270
276
277 (5)
275
274
275
279
278 (10)
276
276
281
277
281 (15)
267
279
275
270
284 (20)
296
292
287
274
262 (25)
244
231
226 (28)
---
---
---

And Test #4 - I removed the hardline and replace with macroline. I initially put the hardline on, without testing, hoping that the size of the line would help me get a high shot count. Wow, to my surprise it had little to do with the number of shots I got. 28 registered shots seems to be the magic number.

272
270
269
274
277 (5)
277
279
274
271
277 (10)
278
280
276
279
273 (15)
274
274
273
281
292 (20)
282
277
268
266
251 (25)
246
232
227 (28)
---
---
---

Something that I can't explain yet I find interesting is in the first test, I didn't adjust anything since playing with it a week ago. It was shooting ~280+ and registered 28 shots. And after I adjusted down to ~280's, it still only registerd 28 shots. Is the valve more efficient at that higher FPS? I don't know. Looking at the numbers, at the higher velocity, the velocity spike occurs at around 15 shots then slowly comes down. At a lower beginning velocity, the velocity spike occurs at around 20 shots.

[Pacifist_Farmer]

Hazarding a guess...

As you consume the CO2 in the system you are approaching an optimal point for expansion of the gas at the given shot interval.

By running at a higher initial velocity more CO2 is consumed with each shot, reaching the optimal point faster.

It's likely that the difference in gas used over 15/20 shots could account for later velocity drop using a lower velocity, but not be sufficient to increase the number of total shots per 12 gram.

It appears that the shots made a higher velocity setting were more consistent, unfortunately they would be too high at the fields I play at.