choking a barrel for improved accuracy

[shorty]

Barrel work for accuracy is my least favorite home brew thing to work on. Too me, it's a lot more precision time consuming work (if you know what your doing). I have read as much as I can with older posts and our grandfathers ways of introducing a choke ( I think ).

So we all know that a good polished lead and good crown makes for a good barrel but, the choke puts the icing on the cake when it comes to pellet variety accuracy.

I have one of those marauder .22 barrels that only like the 21.14 match and I want to try to make it more accurate with other pellets. Now, when I say accurate I mean one hole 5 shot groups at 30 yards ( well atleast a clover group ). 1 shot kill hunting .22 (no fluff).

Well,
Since I have the mini-lathe and an old .177 barrel I tried the wedding band method without heating the wedding band and taping it on. Boy I tell you it does reduce the ID of the barrel. I made the wedding band .005 tighter than the barrel with a 30 degree chamfer and tapped it on approximately .5". To my surprise, the ID shrunk almost the same.
Since I thought I was successful with producing a choke, I ripped apart my trail np .22 and did the same since it hates chp's. I was finally able to do some accuracy testing with the trail and I did not see any improvement. little to no velocity drop with a .5" long  mean choke.

So back to the marauder (or any barrel), does anyone have the insight of the 5 why's for improving the accuracy with a stubborn barrel ? I really want to choke this marauder barrel further than what it is but I fear I will only do more damage.

Note:
If anyone is wondering about my marauder converting back to .22 it's because that .357 is way too loud and I kind of crushed/dimpled the rifling due to the thin wall thickness when tightening down the set screws as Bob said "BE CAREFUL NOT TO CRUSH THE BARREL WITH THE SET SCREWS" Accuracy went to *(&^ after that torqued on those set screws). Just couldn't fix that so I went back to .22.

[Bill G]

experiment is what I'd say.  the .22 Marauder barrels are cheap from what I understand.   

[rgb1]

Concerning the Trail, you haven't said anything about the condition of the
bore.........some thing you would learn thru slugging. There is a fairly good
chance you'll find that the first couple of inches have an ID slightly smaller
than the remainder.......a result of being pressed into the breach block.
The catch is, that until the tight section is relieved thru lapping, the remainder
cannot be reliably checked.
I'm not familiar with  Crosman barrel quality but I can offer this: a good
uniform bore only needs a few tenths of choke. Any more doesn't seem
to help. Here's what I have used on unchoked LW blanks with good results.

  http://104.131.46.156/nextcloud/index.php/s/ELIQ88poBN3Iqy1

Hope this helps.

                                                                     Ron

[Slavia]

Did you happen to measure the amount of choke with the collar?

[rgb1]

The pictured three screw version  produced .0004-.0005 bore constriction.
Using two 4-40 screws in an altogether different piece gave .0003. I might
add......they were very tight.

                                                                                Ron

[K.O.]

well I have only choked one barrel a 2100b straw barrel and I did it by accident... using a nylon spacer/barrel stabilizer... before it did well with CPHP and CPUM and pretty good with 7.4g Crosman pointed, after it was a laser with the 7.4g Crosman pointed but no longer did well with anything else... Big Bore Bart  then used that barrel for his 2100 PCP and stated it was a laser...with Winchester 9.8g and others...

Now I believe pellet barrels can use a choke to good effect because of loose pellet manufacturing tolerances... but I believe a non choked  taper lapped barrel can also do very well with the right ammo... at long distance it may even outshoot the choked barrel...

BUT  you have to start with knowing exactly what you have... oversize bore or undersize, any tight spots, rough spots etc...

Springer/gas struts do not need a choke but a nice taper lapping is a good thing...

I think the Mrod .22 barrels could have a combo of problems, an one is that they are to thin walled( about .11")and low carbon for more than 20-24 fpe but that is my opinion...

I have also read that they can be oversized ~.218" so if you have a .217 or smaller pellet head size it has a good chance of leaving the barrel slightly cockeyed even with the choke...

I think L.W. says that their choke is about/up to .05mm/.00196in

http://www.lothar-walther.com/163.php

just to tight of a barrel can cause accuracy probs at distance also as can a really tight choke...

so yep have to know what you are starting with first... and it is my belief that unchoked is better but needs the right pellet/slug...

[K.O.]

Concerning the Trail, you haven't said anything about the condition of the
bore.........some thing you would learn thru slugging. There is a fairly good
chance you'll find that the first couple of inches have an ID slightly smaller
than the remainder.......a result of being pressed into the breach block.
The catch is, that until the tight section is relieved thru lapping, the remainder
cannot be reliably checked.
I'm not familiar with  Crosman barrel quality but I can offer this: a good
uniform bore only needs a few tenths of choke. Any more doesn't seem
to help. Here's what I have used on unchoked LW blanks with good results.

http://i915.photobucket.com/albums/ac351/rgb_1/chokecollar.jpg?1449579796550&1449579797664&1449579813451

Hope this helps.

                                                                     Ron

I think you meant thousandths..

[K.O.]

The pictured three screw version  produced .0004-.0005 bore constriction.
Using two 4-40 screws in an altogether different piece gave .0003. I might
add......they were very tight.

                                                                                Ron

When I see measurements that small 3-4-5 ten thou I can not help but ask measured how?

[shorty]

I for one surely can not measure (accurately) ten thou (repeatably) and I have some pretty expensive measuring equipment at work.

Experimentation does sound like the only thing at this stage to fix the .22 marauder barrel if possible. It always seems like the people that have tried "working" their barrel have just went through a barrel lottery with crossman or just got a LW barrel for the fix.

I think I am just going to try and measure the existing choke and if it is less the .002" I will leave it and deal with it. If there is little to no choke, I am gonna re-do the choke.

One question though, does choke length matter and if someone had to guess or has some data on choke length please share. I was considering making the sleeve up to 2 inches and test at every .5" of induced choke.

[K.O.]

I have a couple of the sale AF L.W. barrels a .177 and .22 I will measure in a while but I think they are about .75" long...

I also have a choked 1950s Berreta made .22LR ( all the way down to .212" land and .218" groove( L.W. pellet spec) and it is choked about 1" from the muzzle...Designed for 40g and ~100fpe?...

I am curious about my .25 Mrod's choke but it shoots so well I do not want to mess with removing the shroud...

I think if I was to try to fix a .22 Mrod barrel the first thing I would do would be sleeve it and put it in a .25 breech. wonder if brass tube would give it the right stiffness/weight to  tame/minimize harmonics a bit...

https://www.onlinemetals.com/merchant.cfm?pid=1548&step=4&showunits=inches&id=84&top_cat=79&gclid=CPnd95-CzskCFcRgfgodIvME3A

or maybe stainless
https://www.onlinemetals.com/merchant.cfm?pid=14744&step=4&showunits=inches&id=312&top_cat=1

http://www.gatewaytoairguns.org/GTA/index.php?topic=87080.20

http://www.gatewaytoairguns.org/GTA/index.php?topic=83883.0

??

[Pete]

Spin the end of the barrel in a rollor steady.... tighten it up as it spins....

[Rocker1]

That wll work Pete, How is my Kiwi friend doing?   David

[michaelthomas]

Ground gage pins are available in .0001" increments.  That is how you can be able to measure down that accurately.  You can purchase z class gage pins in .0005 +/- increments from Meyer Gage for maybe 4.00 each.  The plus/ minus pins vary a tenth or so of the specified number in the direction they show.  So if you want to check a hole that is about .173.... Buy a .1735+, .1735-, .1730+, .1730-, .1725+, .1725-....etc.  That will be adequate to figure out what you are looking at.

Mike

[rgb1]

This is how I do it. Use the largest pin that will insert
and measure the clearance with an indicator. Very
repeatable.

[Airsnipe]

How do you measure the clearance with the indicator? Wiggle the pin and measure the deflection and add that to the pin dia? Seems like there could be a lot of error with that.

[shorty]

Sure looks like those gauge pins would work. I was taking it the wrong way. Where I work we make extremely fine wire down to .0004". I just got done with a R and R gauge study for some .00079" wire and it failed miserably with a hand micrometer. Only way it would have an acceptable ppk would be with a non contact dual axis laser micrometer that is accurate out to 6 significant numbers. (BORING)

Anyway,
With the donor trail np, accuracy did not improve. So it got me thinking about the brass washers I used a long time ago on the cocking assembly. I pulled them out and measured them and sure enough they where worn (grooved) and .002" different (it's a beater gun). I then turned down some new washers/spacers a little bit bigger (.065" thick) and popped them in.

Unfortunately it is dark now but, I was able to get off atleat 10 rounds at 10 yards and it's  looking good.


I honestly know this is stupid but, I can't justify turning down the .22 marauder barrel when 21.14's shoot one holers. It just makes me PO'ed  that it doesn't shoot anything else that good.

It makes me wonder if LW barrels shoot just about anything accurate and if your a marauder owner should you just spit out the money for one.

[K.O.]

yep they do work I just did not know what he had to measure with... me I muddle thru with push thrus and verniers but that does not mean I

do not know about pin gages or throat erosion gages etc... but honestly Tuning a barrel can be done by feel and measuring .001-.002 differences

Now the pin gages would help figure tuning the right amount of choke to help create a choke that worked well with slugs and still helped pellets... knowing if it is choked .0015 or .0018 or .0021 could be important...

[shorty]

Thanks for all the ideas and encouragement to choking the in-accurate .22 marauder barrel. I found enough courage to wedding band choke the barrel today and I am so glad I did (for now).

Bore is around .217" to .218" and choke was .216" to .217" Measured with dial calipers and slugging the barrel.

Cool thing though was as I was measuring I thought I should stick a CHP into the muzzle head first to see or feel the fit. Too my amazement, the head fell right into the muzzle up to the skirt. I did it a couple times and with other pellets too, and the only ones that felt snug going in was the 21.14 match.

On with the choking,
I turned down the last 1.5" of the barrel to .399" to .398" and made a sleeve with an ID of of .396" to .397" and tapped it on with a mallet. I then faced off the barrel and put an ever so slight crown on it. Polished everything up and re-measured the new choke.

New choke comes out to .214" to .215" measured with dial calipers and slugging again. I re-did the pellet head into muzzle and almost every pellet I have fit ever so snugly to a slight push to get them in there.

I ran 30 chp's at 850fps / 10 yards and again to my amazement, almost one holers. Did another 30 at 10 yards and it was stacking. All I can say is wow!!!!! Gun never dd that before with chp's.

Re-filling the gun now and gonna try to stretch to 25 yards.

[moorepower]

I bought a collet closer to try this.

[shorty]

Using a collet might be a good idea. When I meant tapping on the sleeve with a hammer, the first 1/4" was an easy tap to make sure the sleeve was going on straight. After that, the tapping was getting pretty aggressive to seat the 1.5" collar the whole length. I made the collar approximately a 1/4" longer because I knew it was going to get pounded and it was definitely deformed from hitting it. I just cleaned it up on the lathe after.

Choking takes a lot of force. Another thing was when I was practicing on a 760 barrel, I put a sleeve on,measured the choke to make sure there was something there and then turned down the sleeve to remove it. When the sleeve got thinner and then finally removed, it appeared as if there was no longer a choke. Almost like the metal did not go past it's yield and "sprung" back to it's original shape.

With that being said, I am curious if this is one of the "root cause" problems with the barrels in the first place. Crossman may be using a really good (consistent) tool to choke the barrel but the mechanical properties of the barrel material could be the problem being inconsistent when shaping.