Author Topic: 200 yard mrod  (Read 1884 times)

Truckr6969

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200 yard mrod
« on: March 16, 2016, 05:47:11 AM »
What would it take to make a 25 mod a 200yard gun


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match

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Re: 200 yard mrod
« Reply #1 on: March 16, 2016, 07:10:19 AM »
I am trying - once I get there I will let you know ;)

I am trying to get 35-48-ish gr bullets (nielsen,ratsniper,bbt's) to go 930-960 fps at the muzzle with as little variance as possible. With the BC's of these bullets 200 yrds should be reasonable to achieve within 2 MOA.

My current approach:
got the WAR valve to increase power  (look at the Cothran?)
get an SSG to improve efficiency - ordered Gen I from Travis
maybe a longer barrel (I am thinking about a 26 inch one from Jim Gaska)
got an air tube extension for more shots (I want 12+ within 2%) (look at bottle or double tube?)
t-port mod? (only if needed)

my first step is finding a new leak....
.40 Badger (arrived!)
.25 Gen I MRod w/WAR valve/SSG & MM custom t-port @ 0.17 (Cothran valve on deck)
.22 1322 upgraded to 2289
.17 Webley Hurricane
.17 Daisy 853
.17 late '60's Crosman Powermaster 760 in the original box

rsterne

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Re: 200 yard mrod
« Reply #2 on: March 16, 2016, 08:26:24 AM »
Most guys that are shooting at well over 100 yards are tethering their guns to a regulator and then tuning for a few good shots off-reg.... It becomes very important to keep the ES to a minimum at long range to avoid vertical stringing of the groups.... ChairGun has a widget that deals with that, and you can experiment with it to see how narrow an ES you need to meet your requirements.... With a BC of 0.100, at 100 yards, with a 2% ES, you can expect about 7/8".... which increases to 3.6" at 200 yards.... Reduce the ES to 1%, the vertical stringing at 200 yards reduces to about 1.8".... barely within your 2 MOA goal....This emphacizes the importance of maintaining a constant velocity, which is why guys tether to a regulated tank....

Using bullets instead of pellets will drastically reduce the effects of wind, of course, because of the much higher BC.... The velocity you end up choosing will be a compromise between a flatter trajectory and less wind drift.... because the minimum drift at 200 yards will take place with a muzzle velocity of under 900 fps.... When tuned for the best power / efficiency combination on a tether, you will get maybe 3-5 shots within a tight ES off the tether, because you will be tuned at the top of the sweet spot.... Ninja make a good tank / regulator combination for tethering, with a 2900 psi output reg. on a 90 CI, 4500 psi tank....

Bob
« Last Edit: March 16, 2016, 08:58:09 AM by rsterne »
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match

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Re: 200 yard mrod
« Reply #3 on: March 17, 2016, 07:13:24 AM »
2 MOA at 200 yrds is 4 inches. the vertical stringing is why I said 2 MOA.

Now this is just the limit of the GUN - not the system (shooter, gun, and wind) that error will be a bit more than 2 MOA.

My realistic goal for the system at 200yrds is keeping it under 4 MOA untethered. 

Also you can subgroup the 12 shots and compensate for each subgroup's POI to reduce the vertical stringing impact across the 12.

Knowing your current pressure will be very important to keeping the POI/POA shifts in line.

One last item on the list is a very good quality scope with a mildot or MOA type reticule to adjust POA.

.40 Badger (arrived!)
.25 Gen I MRod w/WAR valve/SSG & MM custom t-port @ 0.17 (Cothran valve on deck)
.22 1322 upgraded to 2289
.17 Webley Hurricane
.17 Daisy 853
.17 late '60's Crosman Powermaster 760 in the original box

rsterne

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Re: 200 yard mrod
« Reply #4 on: March 17, 2016, 08:48:56 AM »
Sorry, I generally try and keep my vertical stringing to half the group size to negate the effect; as you say, 2 MOA at 200 yards is 4".... If you compensate for POI change, then certainly you can use a larger ES.... If you are looking at 80ish FPE in .25 cal, I would suggest all your porting be 3/16" minimum with a 1/4" throat.... Both the W.A.R. and Cothran valves are probably at least that big anyway.... 12 shots at that power is roughly 1000 FPE, so if you have 1000 CI of usable air (within a pressure drops that will keep within your ES), you should be able to accomplish that.... An MRod reservoir is 13 CI, so that would mean a pressure drop of about 1100 psi, which might lead to too large an ES, so you will likely need that extension, double tube, or bottle to keep the ES within reason....

If most of your shooting will be from a bench, and you have a pony tank to top up in the field, I would still use the approach of tethering @ 2900 psi, with a short shot string of very narrow ES off tether.... My Disco Double, with 250 cc of air on tap, gives 14 shots at 88 FPE within a 4% ES, from 3000 psi down to 1800, with 51 gr. BBTs.... that with 0.219" porting and a 0.266" throat.... Alternately, I can tune it for half that many shots at 100 FPE, within less than 2%, and shoot off a tether at that power until the tank drops below 2500 or so....

Bob
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Truckr6969

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Re: 200 yard mrod
« Reply #5 on: March 17, 2016, 07:28:32 PM »
My mrod 25 has war valve SSG and a 3/16 barrel port going to try and tune it to be 975 to 1000fps with 45gun bullets what I'm hoping for is a 25 that can reach out and touch the yotes that have got wise to the electronic call I had on Saturday morning hanging out at 189 and would not come in  any closer looking into the nijah for a teather bottle..... Will know more when new chrono gets here had to send old one back cause it would not read anything
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Dairyboy

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Re: 200 yard mrod
« Reply #6 on: March 17, 2016, 07:55:34 PM »
To be able to get that many shots at that high of speed will be difficult let me know how you do it if you can. I'm able to get 8 shots at 80fpe with 47gr neilsen swaged slugs with 2.1%. I have a 8 shot 72fpe tune with 34gr slugs with I believe 0.7% ES. WAR valve with NBH custom spring and .187 TP with 25" .25 acp barrel and a res extension.
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John 3:16

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