Comparator trick
- Thread starter Tesoro
- Start date
jghoghunter
Gold $$ Contributor
Accuracy One comparitor works well
6BRA
Gold $$ Contributor
They've been on backorder. Measures off shoulder vs base...waiting on mine. These work with most calibers as well unlike instant indicator.
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IMHO anything you have to bind to a caliper has the potential to introduce error. Add two of these and your setting yourself up for worse. The less parts, the better. I have struggled with the 'flex' that exists in multi caliber solutions such as the Forster Datum Dial kit. I switched to using the case-specific comparators (shoulder bump gauge) Whidden supplies with their dies but still need a better solution for loaded cases and bullet comparison. I was simply going to buy their bullet comparators but I like the look of the Accuracy One comparator.
jghoghunter
Gold $$ Contributor
Doesn't seem to be. It is very repeatable. Very easy to use. I don't make a habit of pounding on it.
Its stated that it does not work well for 223 and smaller cases, I don't believe it works on really large caliber either havent checked don't know. It can be used on 223 cases but you need to be really careful. Any larger than 223 it works great.Thanks. I shoot currently 223, 6mm Creed, 308 and, less so, 7mm Rem Mag. I assume 223 cases, particularly, have potential for a lot of 'wiggle' given the size of the case aperture required for 30 cal, hand held only support at the cartridge base and limited shoulder area for contact with the comparator. You've kind of got a comparator that's like a caliper but one jaw being your hand. If you're not holding the case completely concentric against comparator you'll have issues.
Presumably the bullet stem is cut for various calibers also. Is the stem changeable? I saw one advertised with a bullet specific stem.
Presumably the bullet stem is cut for various calibers also. Is the stem changeable? I saw one advertised with a bullet specific stem.
I just ordered a complete set of these today.
This is also what I use
Presumably the Accuracy One tool doesn't have shoulder angle cut into the comparator, only the shoulder datum, e.g. 0.330", 0.400"? It can't because various calibers of the same shoulder datum have different slopes. I see a significant benefit to the Short Action Customs design where contact with the case is the full shoulder area rather than a single circle point of contact. Whidden's aluminum shoulder bump gauges which come included with their dies would benefit from adding this shoulder angle into their gauges also. Having that slope in the comparator would make it much easier to ensure the case is sitting properly.
With the SAC comparators, however, I worry about play between the insert and the body as this is dependent on how snug the o-ring fits, particularly as the o-ring wears. Thoughts?
I like the sound of measuring shoulder to o-give with the Accuracy One coupled with not having to pick up calipers and wiggle/twist cases within the jaws. Shame it tries to be one-size fits all and loses the benefits of greater surface contact area, particularly when your hands don't automatically hold the case concentric with the comparator (as opposed to caliper jaws).
(IMHO there is plenty of surface area on a caliper jaw, at least with mine, to make sure a case is flat to them without introducing the risk of play by screwing an additional piece to one end.)
With the SAC comparators, however, I worry about play between the insert and the body as this is dependent on how snug the o-ring fits, particularly as the o-ring wears. Thoughts?
I like the sound of measuring shoulder to o-give with the Accuracy One coupled with not having to pick up calipers and wiggle/twist cases within the jaws. Shame it tries to be one-size fits all and loses the benefits of greater surface contact area, particularly when your hands don't automatically hold the case concentric with the comparator (as opposed to caliper jaws).
(IMHO there is plenty of surface area on a caliper jaw, at least with mine, to make sure a case is flat to them without introducing the risk of play by screwing an additional piece to one end.)
dgeesaman
Gold $$ Contributor
Standard tools and methods align by the base and measure to the highest point on the shoulder ogive. Perhaps it’s better to contact additional points on the shoulder above and below the ogive, but I think it adds complexity to solve a problem that doesn’t exist. We know the shoulder angle of the brass matches the chamber consistently. Current tools measure base to ogive within .001” consistently and quickly, and we know the goal is not to achieve the closest possible fit to the chamber.
This idea has been around a long time, beginning with using the chamber reamer to make a measure tool from leftover barrel stub. The stub should be superior to a tool made up of generic shoulders, and yet these are generally not considered “necessary” by winning shooters.
I don’t know why I get good data from the Hornady comparators while others do not. Perhaps it’s because I use good mics. I can’t imagine investing in a tool set like the SAC tools without at least a set of Mitutoyo digitals to measure with. There’s way more going on inside of a micrometer than the anvil attachments.
I use a Mitutoyo caliper. And I have a reamer cut from the barrel stub for one of my rifles (unfortunately it's not cut to fit onto calipers making it more difficult to use).
x47Mike - it's a single point of contact while holding the other end in your hand versus aligned in a caliper jaw.
My point is the original poster found a solution to a problem that doesn't exist. The greater issue is play in the pieces attached to the calipers. The Forster Datum Dial kit is a pain in this regard. The Accuracy One tool is handheld against a circle of contact at the other end. As a result I'm not surprised it's very difficult to use with smaller calibers. (However I like the notion of measuring cartridge shoulder to bullet ogive instead of CBTO.) The SAC gauges achieve ease of use/alignment by cutting the shoulder into the gauge but how much play is in the insert to body fitting? I'm looking for a solution to ditch the Forster. The Whidden shoulder bump gauges provide that for CBTS measurements (although I wish they cut the shoulder into the gauge as that would make them easier to use). Currently I still have to use the Forster for CBTO measurements. (In all cases the Mitutoyo calipers have plenty of surface area on their jaws for the base of the cartridge to align to.) I'm leaning towards trying the SAC as the notion of achieving concentricity with the gauge when simply handholding the cartridge base when using the AO gauge concerns me. If they cut the shoulder into their gauge this concern would dissipate a lot.
x47Mike - it's a single point of contact while holding the other end in your hand versus aligned in a caliper jaw.
My point is the original poster found a solution to a problem that doesn't exist. The greater issue is play in the pieces attached to the calipers. The Forster Datum Dial kit is a pain in this regard. The Accuracy One tool is handheld against a circle of contact at the other end. As a result I'm not surprised it's very difficult to use with smaller calibers. (However I like the notion of measuring cartridge shoulder to bullet ogive instead of CBTO.) The SAC gauges achieve ease of use/alignment by cutting the shoulder into the gauge but how much play is in the insert to body fitting? I'm looking for a solution to ditch the Forster. The Whidden shoulder bump gauges provide that for CBTS measurements (although I wish they cut the shoulder into the gauge as that would make them easier to use). Currently I still have to use the Forster for CBTO measurements. (In all cases the Mitutoyo calipers have plenty of surface area on their jaws for the base of the cartridge to align to.) I'm leaning towards trying the SAC as the notion of achieving concentricity with the gauge when simply handholding the cartridge base when using the AO gauge concerns me. If they cut the shoulder into their gauge this concern would dissipate a lot.
6BRA
Gold $$ Contributor
I have mitutoyos as well. The problem lies with the cartridge base. You can measure the same cartridge, 3 different times and come up with 3 different measures. Not by much. You almost have to spin/wiggle the cartridge base to achieve perfect flat. By that time your ogive is scored or stuck on the other end. My accuracy one is in the mail. It sure appears by the video to make life easier. I can only say , WIll ADVISE....
The Sinclair comparator is an excellent unit also. Ive had great results with it.
Please let me know. (Ideally also try some 223 if you have it.)
I'm not quite following how you use the machinist bar. Could you post a photo please.
Blackthorn
Silver $$ Contributor
For a little different perspectives: https://forum.accurateshooter.com/threads/sac-comparator-what-am-i-doing-wrong.4055801/ I wasn't happy with the customer service at sac and the 30% restock fee is ridiculous for a just out of the box and defective product. From my perspective, the o rings weren't the right size on some of the inserts, and those inserts would literally fall out of the stand if tilted while others stayed in place.
Threat of credit card dispute cured the 30% restock fee.
I'm currently waiting for the AC1 comparator and have been using the hornady system. No small anvil and it works. Problem is that it is rather time consuming and hopefully, the AC1 will remedy that.
I have used the Redding dial comparator for 6.5 CM and it works really well. It served well to confirm what the hornady comparator was showing.
Threat of credit card dispute cured the 30% restock fee.
I'm currently waiting for the AC1 comparator and have been using the hornady system. No small anvil and it works. Problem is that it is rather time consuming and hopefully, the AC1 will remedy that.
I have used the Redding dial comparator for 6.5 CM and it works really well. It served well to confirm what the hornady comparator was showing.
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