Author Topic: NOE 250-27-RF (Read 8994 times))

Madd Hatter · « **Reply #180 on:** August 03, 2021, 06:55:51 PM »

Well, I'm now sure my accracy problems are the now cast hunter pellets. I slugged the barrel and got.2635 groove diameter and the pellets are coming in at.250 - .252. I need at least .254 to get the bore to seal. I guess I need to call Al and see about getting this fixed.

EdinGa · « **Reply #181 on:** August 03, 2021, 07:40:49 PM »

Quote from: Madd Hatter on August 03, 2021, 06:55:51 PM

Well, I'm now sure my accracy problems are the now cast hunter pellets. I slugged the barrel and got.2635 groove diameter and the pellets are coming in at.250 - .252. I need at least .254 to get the bore to seal. I guess I need to call Al and see about getting this fixed.

He asked me to send mine back with some pellets I had cast with it. I haven't had a chance to do it yet though. Got my 39 grain slug mold yesterday, so I'm not in a hurry to sort out the pellets.

rsterne · « **Reply #182 on:** August 03, 2021, 08:30:49 PM »

I have never heard of a .25 cal airgun barrel that is larger than a .257 cal PB barrel, and they measure 0.257" groove and 0.250" land.... LW barrels are 0.248" land and 0.254" groove, and smaller at the choke....

I would suggest that for some reason, your barrel is grossly oversize.... Factory pellets would also rattle around in there....

Bob

EdinGa · « **Reply #183 on:** August 03, 2021, 08:40:31 PM »

Quote from: rsterne on August 03, 2021, 08:30:49 PM

I have never heard of a .25 cal airgun barrel that is larger than a .257 cal PB barrel, and they measure 0.257" groove and 0.250" land.... LW barrels are 0.248" land and 0.254" groove, and smaller at the choke....

I would suggest that for some reason, your barrel is grossly oversize.... Factory pellets would also rattle around in there....

Bob

I'm beginning to think that my issues with this mold are undersized and out of round heads. I'm about to post my results with my new .249 39 grain slug mold.

Greg_E · « **Reply #184 on:** August 03, 2021, 11:48:06 PM »

Just bought a used hot plate on eBay for trying to keep the mold at a better temperature, won't be testing these again until it arrives. This is what I bought, $54 including tax and shipping, just hope it really works well enough to sustain around 400 to 500 degrees. https://us.vwr.com/store/product/4778117/barnstead-thermolyne-electric-hot-plate-type-2300-thermo-scientific

EdinGa · « **Reply #185 on:** August 03, 2021, 11:54:44 PM »

Hotplates definitely help. I followed the advice of others and put an old circular saw blade on top of burner to sit the molds on. If you can find a metal coffee can or something similar, cut an opening at the top and turn it upside down over the molds to create an oven effect.

Back_Roads · « **Reply #186 on:** August 04, 2021, 12:10:03 AM »

I also had better mold pre heat results with a hot plate with a buffer plate made from a heating plate salvaged from a coffee maker, amd added a sextion of stainless chimney adapter for wood stove from hardware store as a retention device topped with on3 of my salvaged cast iron fry pans that fit the diameter of the hot plate burner, can heat to temp one mold and start the preheat on another while warming up the first mold then while casting one size etc. drop the 2nd mold into the lower hotter section to finish to temp for the next style pellet/ slug for the next needed batch. Alxo use this for mold break in multi tasking is my way do go.
Anyone needing a good read should read the GTA like I do

ps ok maybe I do not type so well since now they call it keyboarding

BTW this AM I ran out of now info or things I was able to help with so started reading post from the beginning of GTA new site in reguards to slug shooting and other things I was wanting to see how things have changed or stayed the samish.

rsterne · « **Reply #187 on:** August 04, 2021, 01:11:12 AM »

The head often doesn't seal in the bore anyways, in fact with many pellets it barely rides the top of the lands.... It is the skirt that seals, and usually it blows out to fill the rifling anyways.... Here is a photo of JSB Pellets, the two on the right were pushed through the bore, and the two on the left were fired....

Note that there are hardly any rifling marks on the head of the pellet, and that they are not very deep on the skirt of the unfired ones.... Also, note how much the skirt has blown out to match the bore on firing....

Bob

EdinGa · « **Reply #188 on:** August 04, 2021, 01:16:54 AM »

Quote from: rsterne on August 04, 2021, 01:11:12 AM

The head often doesn't seal in the bore anyways, in fact with many pellets it barely rides the top of the lands.... It is the skirt that seals, and usually it blows out to fill the rifling anyways.... Here is a photo of JSB Pellets, the two on the right were pushed through the bore, and the two on the left were fired....

Note that there are hardly any rifling marks on the head of the pellet, and that they are not very deep on the skirt of the unfired ones.... Also, note how much the skirt has blown out to match the bore on firing....

Bob

I see what you mean. I guess I was right in blaming the undersize skirts in the first place then.

Greg_E · « **Reply #189 on:** August 04, 2021, 10:58:36 AM »

Take a tin that has been abused in shipping and has bent skirts, now shoot them and see what kind of accuracy you get. Undersized, especially in one area, will definitively wreck accuracy.

If the skirts were uniform but undersize, I'd expect lower velocities from the air getting around the skirts. But I'd also think that you might get vertical strings because I'd like to think the horizontal accuracy might be OK.

Nvreloader · « **Reply #190 on:** August 04, 2021, 12:25:33 PM »

Ed
Here is some info I found when comparing 25 pellets, unfired and fired and caught with no pellet damage.

Unknown brand name of 25 cal pellet, (soft lead)
the unfired pellet had overall length of .353",
the recovered fired pellet had an overall length of .348".

The obturation ring on the pellet skirt was approximately .055 to .060" in width,
(the edge of the pellet skirt that sealed the bore).

Have you fired and caught any of the undersized NOE pellets and measured for results etc?

I'll have to find the rest of the fired collection.......

Tia,
Don

subscriber · « **Reply #191 on:** August 04, 2021, 06:09:32 PM »

Looking at Bob's pellet images above:

The skirt is thin, and relatively unsupported at the open end. Thus, pushing the pellet through the barrel just sizes the skirt down into the skirt's "open space" at low force, without producing a long line of hard engagement at the skirt OD.

When you shoot the pellet, the air pressure inside is not only offering support to counter that sizing down force, the air pressure is actually "blowing the skirt out", until there is enough support from the barrel to prevent further deformation.

If the skirt thickness were increased at its open end, then pushing a pellet through the barrel should produce a slightly longer line of engagement with the groove diameter. If the skirt were solid, that would produce more significant engagement than the already solid pellet head; because the head is usually smaller in diameter than the skirt.

I notice that pellets shot into clay from my Baikal MP 46M seem to have a very short line of engagement at the groove diameter of the barrel. I think this is because this 4 FPE SSP probably generates less than 1000 PSI from its single cocking stroke.

A 4 FPE springer pistol probably would produce a more spikey pressure pulse, with a longer apparent bearing length at the open end of the pellet skirt. Yes, the interaction between actual pellet skirt and barrel groove diameters obviously matter. For a proper comparison, the same pellets and a very similar barrel land and groove form and diameter should be used.

Bottom line: When pushing a pellet through (the unchoked portion of) a barrel, I want to see a clean, even, unbroken ring of hard contact between skirt OD and barrel groove diameter. That contact witness ring does not need to be longer than perhaps 0.01" to satisfy me that the pellet skirt is large enough to work when actually shooting it.

Nvreloader · « **Reply #192 on:** August 22, 2021, 03:54:01 PM »

Ed
And any others that have the 25 NOE molds,

Haven't hear from you lately........

What was the best size of your pellets skirts on the 25 cal NOE mold?,
would a max of .258/260" diameter work better?

I am working on getting the BEST skirt diameters possible, in all calibers from 177 thru 25,
along with the guy running the sizing program, he is the brains,
we added the Best skirt sizing for the LW barrels also, so should have all the bases covered.......I hope.

Thanks,
Don

EdinGa · « **Reply #193 on:** August 22, 2021, 04:02:22 PM »

Quote from: Nvreloader on August 22, 2021, 03:54:01 PM

Ed
And any others that have the 25 NOE molds,

Haven't hear from you lately........

What was the best size of your pellets skirts on the 25 cal NOE mold?,
would a max of .258/260" diameter work better?

I am working on getting the BEST skirt diameters possible, in all calibers from 177 thru 25,
along with the guy running the sizing program, he is the brains,
we added the Best skirt sizing for the LW barrels also, so should have all the bases covered.......I hope.

Thanks,
Don

I haven't had time to cast anything lately, but I can tell you that my Flashpup loves AA 25.4s and the skirts on them measure .258 to .260.

subscriber · « **Reply #194 on:** August 22, 2021, 09:08:15 PM »

Quote from: EdinGa on August 22, 2021, 04:02:22 PM

I haven't had time to cast anything lately, but I can tell you that my Flashpup loves AA 25.4s and the skirts on them measure .258 to .260.

My impression is that Hatsan barrel bores tend to run on the large side. Is that a good generalization? If so, what head diameter does you Flashpup prefer, Ed?

EdinGa · « **Reply #195 on:** August 22, 2021, 09:24:24 PM »

Mine seems to prefer .250 heads and it likes .250 slugs.

subscriber · « **Reply #196 on:** August 22, 2021, 09:27:48 PM »

Thanks, Ed

EdinGa · « **Reply #197 on:** August 22, 2021, 09:53:38 PM »

No problem at all. These Hatsan barrels are accurate but they do seem to be a little large.

subscriber · « **Reply #198 on:** August 23, 2021, 12:56:35 AM »

I happen to have an unmodified spare Green Mountain .25 Marauder barrel. Its breech measures .260" up to the middle of the TP (without breech O-ring installed). So, sizing .25 pellet skirts to .258" would not seem out of order. Pellets with .258" skirts will probably take a little push to get past the breech O-ring, but hopefully not enough to cause any trouble. The probe nose at full diameter is .253" on my Gen 2 Marauder.

From a thread I posted a few years back, the Green Mountain .25 barrels have a groove diameter of .254", before the choke. The "chamber" on the stock Marauder barrel is very abrupt. So, it is useful to "throat" the chamber to rifling transition so it is more of a slope than a step. If that has been done, a larger skirt diameter should not be more "catchy" on chambering.

Air rifles with side levers are probably not even going to notice if there is a slightly higher loading force near the end of the stroke.

K.O. · « **Reply #199 on:** August 23, 2021, 03:42:35 AM »

Hmm, both my G.M. gen II .25 are ~.2497/.252 ...are you sure yours is G.M. ; how many lands and grooves...

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NOE 250-27-RF

Author Topic: NOE 250-27-RF (Read 8994 times))